Hello again!!

Hi all,

It's been so long! Long story short, sorta locked myself out of this account and thus...well...haven't been able to post hahahaha. All good now:))

It's been like 8 months so let's recap...

For those asking, I did manage to grab A*s in all three of my sciences:)). Despite this though I only carried on with physics and biology...well...and chemistry too...for a bit (long story)...

Basically with the new A level system I started out with 4 (Chemistry, Maths, Physics and Biology) but our school quickly made us cut down to 3 (much to my sadness) so I decided to drop Chemistry because it's simply the one I didn't need as much (regarding my career path).

I know that sounds a bit strange because I am hoping to read Law at university, but still, Chemistry had to be dropped):

So here we are now, i'm currently mid-way through 1st year A levels (equivalent to AS year) and it's a bit hell at times but mostly all good. What i'm really getting at in this post is whether anyone would like me to do revision blogs such as this one, and my others, for Biology and Physics A level? (I could also do math, but it may be a bit trickier but if you want, I will:D). For biology I do the AQA spec and for physics I do OCR Physics A (maths is also OCR covering the topics Core 1, Core 2, Statistics 1, Core 3, Core 4, and Mechanics 1).

Even if we take different exam boards, it may be useful since a lot of stuff crosses over all boards.

Have a mull over:) tbh I love to do this for the enjoyment of helping people, so let me know if these blogs have/will help you, and i'll continue them:))

Thank you for all your support,

Millie xx

4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

carbon monoxide - greenhouse gas

sulfur dioxide - acid rain

3.8 describe the structure and explain the function of the male and female reproductive systems

Male
Testis - produce sperm cells
Sperm duct (vas difference) - carries sperm to the penis
The prostate gland - adds fluid to the sperm, creating semen
The urethra - carries sperm out of the penis.

Female
Ovaries - produce eggs
Oviduct (fallopian tube) - carry the eggs to the uterus, is the site of fertilisation
Uterus - develops the fertilised egg on the placenta

2.83 describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems

nervous system - electrical impulses
hormones - chemicals

(nervous is much faster than hormonal)

1.2 describe the common features shared by organisms within the following main groups: plants, animals, fungi, bacteria, protoctists and viruses, and for each group describe examples and their features as follows (details of life cycle and economic importance are not required)

Plants
- Are multicellular organisms
- their cells contain chloroplasts
- have cell walls made of cellulose
- they sort carbohydrates as starch or sucrose
-have a nucleus
- they can photosynthesise

Animals
- are multicellular organisms
- cells do not contain chloroplasts
- have no cell walls
-store carbohydrates as glycogen
- have a nucleus

Fungi
- some are multicellular, some are single celled
-have cell walls made of chitin
- store carbohydrates as glycogen
- their body is organised into a mycelium made from thread-like structures called hyphae which may contain nuclei
- can not carry out photosynthesis (and therefore do not contain chloroplasts). Instead they feed by saprotrophic nutrition (extracellular secretion of digestive enzymes onto food material and absorption of the organic product


Bacteria
- all are single celled
-have a cell wall
- lack a nucleus but contain a circular chromosome of DNA (a plasmid)
- some can carry out photosynthesis, must most feed of living or dead organisms

Protoctists
- all are single celled
- some have chloroplasts (but some don't)
- some have features like animals (for example, no cell wall) whilst others have features like plants (for example, have a cell wall)

Viruses
- they have no cellular structure (so are not even single celled)
- they have a protein coat
- they contain one type of nucleic acid (either DNA or RNA)
- can not photosynthesise. They are parasitic and can reproduce only inside living cells. They infect every type of living organism.

Examples

Plants - maize
animal - human
fungi - Mucor (multicelled), yeast (single celled)
bacteria - lactobacillus
protoctists - amoeba (plant like) chlorella (animal like)
viruses - influenza, HIV

Quick notice

Hi all!

Hope all your revision is going well, I have now finished the spec for biology and am going through each point, editing and correcting any mistakes/typos I have made/you have pointed out (and also learning the points for myself!).

If there are any mistakes I've failed to spot/anything I have got wrong/anything you don't understand please don't hesitate to comment & I will amend as soon as possible :)

Hope all your exams go well,

Millie

2.16 describe experiments to investigate diffusion and osmosis using living and non-living systems.

Diffusion in non-living
- Make agar jelly by mixing phenolphthalein and dilute sodium hydroxide (NOTE: The jelly will be pink from the phenolphthalein, incase you were wondering)
- Fill a beaker with dilute hydrochloride acid
- Cut different sized cubes (e.g 1x1cm, 2x2cm, 3x3cm) and put them in the dilute hydrochloric acid
- Leave the cubes for a whole

you should observe that they go colourless because the acid diffuses into the agar jelly


Osmosis in living
- cut a potato into 5 even cuboids, measure their lengths
- obtain 4 beakers wit different sugar solutions in them, and 1 with just watr (this will be our control)
- put each potato strip into one of the 5 beakers
- leave for 1 hour
- remove potato and measure strips again

Conclusion - if water has entered the potato, the length will be greater, if it has left, the length will be shorter (than before).


Osmosis in non-living

- tie a piece of string/wire around one end of some visking tubing and put a glass tube in the other, fixing it in place with more wire.
- pour sugar solution down the glass tube into the visking tubeing
- put the visking tubing into a beaker, fill the beaker with pure water and make a note of how far up the beaker the waterline sits
- leave the experiment overnight
- return the next day and measure the amount of water in the beaker

Conclusion - the water should have been drawn into the Visking tubing by osmosis, this will force the liquid up the glass tube

3.33 undersand that the incidence of mutations can be increased by exposure to ionising radiation (for exampe gamma raysX-rays and ultraviolet rays) and some chemical mutagens (for example chmicals in tobacco)

Ionising radiation can induce mutations. So can some chemicals in tobacco as
this is why you can get cancer from smoking (as some cancers are a mutation of a cell)

5.20 evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation

When evaluating, you just need to go over the positives and negatives and weigh up which is more (more positives or more negatives)

Positives

- Animals can produce medicines in their milk. Human genes can be transferred into animals to produce human antibodies to fight illnesses such as arthritis, multiple sclerosis and some types of cancer.

- Animals have organs suitable for transplant into humans (e.g. pigs). They could be developed by genetic engineering then cloned.

- Farmers do not have to wait for a 'good animal' like with normal breeding, all their animals could be beneficial with cloning

Negatives

- Cloned animals MAY not be as healthy as normal animals

- Lots of mistakes; embryos from cloned animals often do not develop well/efficiently/normally

- It is difficult, expensive and time consuming

- There may be long term risks that we are unaware of

5.19 describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

Dolly is just used as an example as she was the first cloned mammal. The method is as follows...


- Remove the nucleus of an egg cell. This creates an enucleated egg cell (just a cell without a nucleus)

- Insert the nucleus of a diploid cell of the mammal you want to clone

- shock the new cell by electric shock to start division by mitosis. This creates an embryo

- Implant the embryo into the uterus of a surrogate mother (has to be the same species) to develop.

Now wait for the animal to be born

5.18 understand how micropropogation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics

If loads of plants are required, you can take cuttings from the explants to produce even more plants. It is also very quick so the farmer will not need to rely on the correct conditions like during natural growth - the commercial company can ensure they ill have stock (of plants).

NOTE: the process of micropropogation is explained in point 5.17.

5.17 describe the process of micropropogation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media

Micropropogation is a technique used to clone plants. Here's how it works...

- A plant with desired characteristics is selected to be cloned. Small pieces are cut from the tips of the stems and the side shoots of the plant (these cuttings are known as explants)

- The explants are sterilized to kill any microorganisms

- The explants are grown in vitro. All this means is that they're placed in a petri dish that contains a nutrient medium. This medium has all the stuff the plant needs to grow. It also contains growth hormones (auxins)

- The explant begins to grow and are taken out of the medium and planted in soil.


These plants develop into plants that are genetically identical to the original plant, meaning they will share the same characteristics.

5.16 understand that the term 'transgenic' means the transfer of genetic material from one species to a different species

Transgenic means the transfer of genetic material from one species to another. If something is said to be transgenic, it means  they contain  genes transferred from another species.

5.15 evaluate the potential for using genetically modified plants to improve food production (illustrated by plants with improved resistance to pests)

Crops can be genetically modified to increase yield. For example, making them resistant to insects/weed killers.

Making them insect resistant means farmers can spend less money on chemicals such as pesticides, this also increases yield.

making them resistant to weedkiller means farmers can kill weeds without killing the plant.

However, many people are against genetically modifying foods as there are no studies on long term effects on humans. There are also religious reasons. Also, if a weed gets the weedkiller resistance gene, there will be no way to kill it.

5.14 understand that large amounts of human insulin can be manufactured from genetically modified bacteria that are grown in a fermenter

This is one of the uses of genetic engineering, here's how it works...

- the DNA you want to insert (in this case, the gene for human insulin) is cut out of a human cell using a restricton enzyme.

- The vector DNA (either a plasmid or virus, in this case, plasmid) is cut open with a restriction enzyme.

- the vector DNA and insulin DNA are combined with a mixture of ligase enzymes. The ligase enzymes join the two pieces of DNA together, producing recombinant DNA

- The recombinant DNA is inserted into  a bacterium

- The bacterium is grown in a fermenter


The bacteria cells now make insulin. This is useful to produce insulin on a mass scale for people with diabeties etc.

5.13 describe how plasmids and viruses can act as vectors, whch take up pieces of DNA, then insert this recombinant DNA into other cells

A vector is something that is used to transfer DNA into a cell. The two types of vectors are plasmids and viruses.

Plasmids - small circular molecules of DNA that can be transferred between bacteria

Viruses - insert DNA into the organisms they infect

5.12 describe the use of restriction enzyme to cut DNA at specific sites and ligase enzyme to join pieces of DNA together

Ligase enzymes are used to join together two pieces/strands of DNA, alternatively, the restriction enzyme cuts DNA at a specific point by recognizing the specific sequences of DNA.

NOTE: Two different bits of DNA that have been stuck together is known as recombinant DNA

5.11 understand that animals with desired characteristics can be develope by selevtive breeding

Selective breeding can ensure an animal produces the maximum yield of, for example, meat/milk, has good health/disease resistance, has good mothering skills, not a bad temper, is fast (good for racehorses etc) and has high fertility.

5.10 understand that plants with desired characteristics can be developed by selective breeding

Selective breeding can be used to combine the best characteristics to produce the best crops.

For example, tall wheat plants have a very good yield but are easily damaged by the elements whereas dwarf wheat plants can resist the elements but have quite a low yield. The two plants can be bred together, ensuring the offspring can battle the elements and have a good crop yield.

5.9 explain the methods which are used to farm large numbers of fish to provide a source of protein, including maintenance of water quality, control of intraspecific and interspecific predation, control of disease, removal of waster products, quality and frequency of feeding and the use of selective breeding

Fish farming is a possible solution to the problem of overfishing. It is controlled and designed in a way to produce as many fish as possible.

NOTE: Everything specifically to do with fish farming in cages in the sea is in blue, everything specifically to do with fish farming in tanks is in green.

Maintenance of water quality
There is a current in the sea so water is naturally kept 'clean'.
The water can be removed, filtered and cleaned. Water can be monitored to ensure temperature, [H and oxygen level is at the best potential.

Control of intraspecific and interspecific predation

Firstly, interspecific predation is being eaten by other animals, intraspecific predation is cannibalism, basically.

Fish farming in cages stops interspecific predation as it means no animals/fish can eat the farmed fish. Big fish and baby fish are kept separate to keep intraspecific predation low.

Control of disease

Fish in cages are prone to diseases such as lice . Biological pest controls are used to control the lice as chemical pesticides can harm the fish.

Removal of waste products

The water can be removed and filtered, getting rid of waste.

Quality and frequency of feeding

A diet of food pellets is carefully controlled to maximize the amount of energy the fish get as more energy = more growth = bigger fish. Furthermore, the better the quality of food, the bigger the fish will grow.

It is easy to control how much food is given, as it doesn't wash away in the current of the sea.

Selective breeding

The fish can be selectively bred to produce fast growing, less aggressive fish, for example.

5.8 interpret and label a diagram of an industrial fermenter and explain the need to provide suitable conditions in the fermenter, including aseptic precautions, nutrients, optimum temperature and pH, oxygenation and agitation, for the growth of micro-organisms

Okay so to start, here is a diagram...

Conditions...

The fermenter must be kept aseptic so only the desired microorganism grows. In order to do this, it is cleansed (usually with steam) before production takes place.

Nutrients are provided to ensure that the microorganisms always have enough food to grow.

The optimum temperature and pH is maintained and monitored with probes (connected to a screen)  to ensure maximum growth. Also, if the temperature is too high, the enzymes will denature. An optimum temperature needs to be kept to ensure the best yield.

If the process requires aerobic respiration (not beer, for example, which requires anaerobic respiration of yeast to make ethanol), there is an oxygen supply.

Agitation/stirring takes place to ensure that the microorganisms, nutrients and temperature are evenly distributed.

image credit: BBC

5.7 undersand the role of bacteria (Lactobacillus) in the production of yoghurt

Lactobacillus is the bacteria that ferments milk (into yoghurt) in yoghurt production. This is the process...

- All equipment is sterilized in order to kill off any unwanted micro-organisms.

- the milk is heated to 72° for 15 seconds (pasturisation) in order to kill any germs in the milk.

- the milk is cooled

- The bacteria 'lactobacillus' is added.

- the mixture is incubated at around 40° in a fermenter. This is where the bacteria ferment the lactose sugar in the milk, forming lactic acid

- The lactic acid causes the milk to clot, causing it to solidify and turn into yogurt.

- Any flavourings/colourants are added

- the yogurt is packed

5.6 describe a simple experiment to investigate carbon dioxide production by yeast, in different conditions

When yeast respires aerobically, it produces carbon dioxide as a bi-product. Here is how to measure the effect of changing temperature on carbon dioxide production from yeast...

- mix together some suger, yeast aand distilled water. Add this mixture to a test tube

- attatch a bung with a delivery tube. Attatch the other end of the delivery tube to a test tube of water

- Put the tube containing the yeast/water/sugar solution in a water bath at 10°.

- leave to warm up for 5 minutes and then count how many bubbles are produced in one minute

- repeat with 4 other test tubes, one at 15°, one at 20°, one at 25° and one at 30°. You should also do one at room temperature as a control

- plot results in a graph and compare/find patterns/anomalies

should all go well, you should conclude that as temperature increases, the rate of respiration (and therefore amount of bubbles) should increase. However, if you have done a water bath past optimum temperature for the enzymes (as respiration is controlled by enzymes), then there will be very little/no data for this tube.

NOTE: You can use the same apparatus but measure the effect on different concentration of sugar, for example, by keeping the water bath the same temp but adding more/less sugar to each tube. the same can be done with volume of water and/or concentration of sugar solution etc

5.5 understand the role of yeast in the production of beer

When yeast respires anaerobically (without enough oxygen) it produces ethanol/alcohol as a bi-product. In beer production, yeast respires anaerobically. It is the ingredient in the production of beer that makes the alcohol, it ferments the sugars into alcohol.

5.4 understand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with crop plants

Pesticides/pest control kills insects/microorganisms/mammals that feed on crops. they are useful as they are very effective. However, they are poisonous to humans so must be used carefully around foods etc (e.g. growing carrots) and some pesticides are harmful to other wildlife.

Biological control is an alternative to pesticides, it involves using other organisms to control pests (e.g. introducing hoverflies to an area to reduce the amount of aphids, as aphids kill hoverflies). This has a longer lasting effect on the crop/area than pesticides do and is less harmful to the ecosystem. However, it can cause problems. for example, the introduced species could become uncontrollable and their predator would have to be introduced to control them. It can also take longer (potentially).

5.3 understand the use of fertiliser to increase crop yield

If plants don't get enough nitrogen, potassium or phosphorus, their growth and other life processes could be affected.

These elements are naturally found in the soil, however, they could be lacking due to previous crops using them up. All fertilisers do is replace them in the soil, so the plants can grow very well.

5.2 understand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses

Okay so, I mainly covered this, along with other factors, in point 5.1, but here it is again...

If carbon dioxide is increased, the rate of photosynthesis will be increased. Meaning more photosynthesis will occur each day, meaning a bigger crop yield.

If temperature is increased, plants can grow throughout the winter and don't die of frost etc. This also lowers the rate of transpiration (as there is a lower concentration gradient inside vs outside the plant leaf so the rate of transpiration is lower).

5.1 describe how glasshouses and polyethene tunnels can be used to increase the yield of certain crops

Glasshouses and polyethene tunnels/polytunnels help to create the ideal conditions for plants, thus increasing the yield (how much grows) of a crop. Some ways they create the perfect conditions are...

- The plants are enclosed, meaning they are at no/a significantly lower rick of pests and diseases.

- Artificial light can be supplied which will increase the time per day a plant is photosynthesizing

- The suns heat can be trapped (particularly in glasshouses). This keeps the plant warm. In winter it can stop the plants from being damaged by frost etc

- As it is an enclosed space, farmers can increase the level of carbon dioxide in the glasshouse/polyethene tunnel. They can do this by burning a paraffin lamp etc (combustion fossil fuels gives carbon dioxide). This further increases the amount/rate of photosynthesis the plant endures.

All of the above increase the yield of a plant.

4.17 understand the effects of deforestation, including leaching, sol erosion, disturbance of the water cycle and of the balance in atmospheric oxygen and carbon dioxide

Leaching

Trees leach nutrients when they are alive, but return nutrients to the soil when they die. When trees are cut down, nutrients gets leached but not returned, resulting in infertile soil.

Soil erosion

When trees are removed, soil can be washed away by rain etc as tree roots hold soil together (but there will be no tree roots, as there will be no trees).

Disturbance of the water cycle

Trees take up water, when they are cut down, water runs straight into rivers, causing flooding. also, the local climate gets drier as there is much less transpiration occurring.

Disturbance of the balance of carbon dioxide and oxygen

When trees die, carbon dioxide is naturally released. When they are burnt, all the carbon dioxide is released at once. alternatively, if wood is used in furniture etc, the carbon is stored and not released, disrupting the carbon cycle.

Fewer trees means fewer photosynthesis means less oxygen.

4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing depletion of oxygen

Like fertilisers, sewage also contains phosphates (from detergents) and nitrates (from faeces etc). If these are leaked into rivers, eutrophication occurs.

NOTE: Point 4.16 my help for understanding

4.16 understand that eutropication can result from leached minrals from fertiliser

Nitrates and phosphates can leak from mineral fertilisers that are put on fields. If it rains, they are easily leached into rivers and lakes. this results in eutrophication. Basically...

- The extra nutrients causes algae to grow super fast. This blocks out the light
- Plants in the river (before the algae) can not photosynthesise due to low light. They die.
- With more food (dead plants) available, microorganisms living in the water rapidly increase in number and deplete/use up all of the oxygen in the water.
- Organisms, like fish for example, that need oxygen, die.

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences

Heat from the sun is naturally radiated off the earth and into space. Greenhouse gases naturally keep in some of the heat (otherwise we would all die of cold, basically). However, increasing the amount of greenhouse gases is blocking the heat from escaping (known as the greenhouse effect). effectively, this heats up Earth, which is global warming.

Consequences of global warming include climate change (e.g. change in rainfall pattern)

4.13 understand how human activities contribute to greenhouse gases

Okay so basically...

Contribution to carbon dioxide - Car exhausts, industrial processes (burning of fossil fuels etc), cutting down of trees

Contribution to methane - rice growing, cattle rearing

Contribution to nitrous oxides - fertilisers, vehicle engine, industrial engines

CFCS - all man-made

4.12 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases

NOTE: You may be asked where the greenhouses originate from. Well, its not in the spec but it was in the 2015 paper so just to be safe I have included the info (its in red).

Greenhouse gases are bad as they trap heat from the sun in the earths atmosphere. Examples of greenhouse gases include...

- Water vapour
- Carbon dioxide (deforestation, industrial processes, car exhausts)
- Nitrous oxide (fertilisers, vehicle engines, natural release from bacteria)
- Methane (rotting plants, rice growing, cattle rearing)
- CFCs (NOTE: CFCS are man-made chemicals, they are basically not produced anymore but some still are and are leaking from old products that contain them)

4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

Sulfur dioxide

When fossil fuels are burnt, sulfur dioxide is released (from sulfur impurities in the fuel). When it mixes with rain clouds is forms acid rain (dilute sulfuric acid). This kills fish and trees as it causes lakes to become more acidic and can damage leaves and release toxic substances from the soil, meaning it is hard for the tree to take up nutrients from the soil.

Carbon monoxide

When fossil fuels are not burnt with enough air (incomplete combustion), carbon monoxide is produced. this is a poisonous gas and binds to haemoglobin in red blood cells, preventing the red blood cells from carrying enough oxygen to your muscles.

4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitryfying bacteria (specific names of bacteria are not required)

Firstly, here's a diagram...



Okay so...

nitrogen fixing bacteria - this turns atmospheric nitrogen into nitrogen compounds (in the soil) that plants can use

decomposers - turns proteins and urea (from plants and animals) into ammonia

nitrifying bacteria - this turns ammonia into nitrates

denitrifying bacteria - this turns nitrates back into atmospheric nitrogen gas

The process repeats.

NOTE: Some of these bacterium live in the soil and some live on the root nodules of plants.

4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

To start, here is a diagram...



Okay so...

Respiration - breathing basically. this releases carbon dioxide back into the air.

Photosynthesis - carbon is taken in (by the plants)

Decomposition - when plants and animals die, decomposers decompose them. this introduces carbon back into the soil

Combustion - things like wood and fossil fuels are burned. This releases carbon dioxide back into the air

The carbon dioxide in the air is then taken in by plants and the cycle continues(this is why plants are so important)

4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation

Firstly, here is a diagram...


Okay, so...

Evaporation - this is where water (from  the ground) gets warmed (usually from sunlight). When this happens, the water molecules gain energy and they start to move lots more, eventually they turn into a gas.

Transpiration - all transpiration is is evaporation from plants/leaves

Condensation - When the warm water vapour is carried upwards (convection currents). However, the higher you go the colder it gets. The water vapour eventually cools down and condenses, forming clouds

Precipitation - a fancy name for rain/snow/hail

4.7 explain why only about 10% of energy is transferred from one trophic level to the next

This is mainly explained in point 4.6, but I will cover the main points again...

Much energy is lost so not all energy an organism takes in is conserved until it dies and then transferred onto he next trophic level when it is eaten. the main causes of energy loss are...

- Heat energy
- Energy needed for the 7 life processes
- Energy in indigestible foods (e.g fibre) is not 'absorbed'

this results in around 90% of the energy being used, so only 10% is passed onto he next trophic level.

4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

Food chain
A food chain shows the flow of energy up the food chain. It can only show one organism at each trophic level, also you cannot tell whether the organism is feeding at more than one.


Here is an example of a food chain...

Food web
A food web gives a better understanding of a certain ecosystem by linking several animals within a habitat showing which organisms consumes which etc. A food web basically just shows multiple different food chains, that are all linked together. They show multiple different trophic levels including multiple prey and multiple predators. This means an organism has the potential to be a secondary or tertiary consumer at the same time.

Here is an example of a food chain...

Pyramid of numbers
A pyramid of number shows the number of each organism (of each trophic level of a certain food chain) by the area of the block in the pyramid. E.g a large block is lots of that animal, a little block means few of that animal.

Here is an example of a pyramid of numbers...

Pyramid of biomass

A pyramid of biomass is a bit like a pyramid of numbers, only it represents the dry mass of each consumer (and producer), again, by the area of a pyramid block.


Here is an example of a pyramid of biomass...

Pyramid of energy

A pyramid of energy, again looks like a pyramid of numbers/biomass, but it shows the transfer/flow of energy through the food chain.

Here is an example...

NOTE: The amount of energy transferred decreases by 10% each time, this is important (this is explained in 4.6).

4.6 understand the transfer of substances and of energy along a food chain

Plants use energy from the sun in photosynthesis, this energy makes its way through the food chain as animals eat the plants and each other.

However, not all the energy that's available to the organisms in a trophic level is passed on to the next trophic level, this is because 90% of the energy is lost in various ways. These include...

- Indigestible energy is not taken in in the first place (e.g. fibre), it is just digested out
- Lots of energy is used for the 7 life processes
- Lots of the energy is lost in heat

NOTE: Only around 10% of energy becomes biomass (e.g. it is stored for growth etc). This is transferred onto the next trophic level once the organism is eaten.

4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers

Producers are the first trophic level because they are at the bottom of the food chain. They turn sunlight into usable energy, in other words, the produce energy.

The second tier are known as the primary consumers, as they are the first consumer in the food chain. They consume the producers.

The third tier are known as secondary consumers as they are the second consumer in the food chain, they consume the primary consumers.

And so on.

NOTE: Eventually all of the above die, they are eaten by decomposers (who break down dead material/waste.

4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats

This experiment is laid out along a line (known as a transect).

-  Mark out a line along the area you want to investigate

- Using quadrat(s) placed next to each other, collect data along the line.

That's it :)

4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas

Firstly, this is a quadrat…

They are usually 1m2 and split up into 100 smaller squares. Just randomly place/throw it on the ground and count all of the organisms within the quadrat. Repeat 5 times and find the mean. Now multiply the number of that organism found with the size (in m2) of the area you are investigating.

Repeat with another area and compare.

4.1 understand the terms population, community, habitat and ecosystem

Population - All the organisms of one species in a habitat

Community - All the different species in a habitat

Habitat - The area/place in which an organism lives

Ecosystem - All of the organisms living in a particular area and all the abiotic (non-living) conditions

NOTE: You literally just need to learn these

3.32 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lean to infections being difficult to control

Bacteria can develop mutations too, this changes the characteristics and some bacteria become more resistant to particular antibiotics. This means they have an increased chance of survival, so it lives longer and reproduces producing lots of bacterium that are resistant to that particular antibiotic. This is just natural selection.

This poses a problem for people who become infected with the mutated bacteria as the bacteria will not be killed off by the antibiotic supplied, that or a new antibiotic will need to be found which takes a long time.

3.31 understand that many mutations are harmful but some are neutral and a few are beneficial

Most mutations are harmful. For example...

- If a mutation occurs in reproductive cells, the offspring might develop abnormally or die
- If a mutation occurs in body cells, the mutated cell may start to uncontrollable divide and become a cancerous tumour.

Some mutations are neither harmful nor beneficial. For example...

- If a mutation occurs in an unimportant part if the DNA it will not affect the person/animal/plant.

Some mutations can be beneficial also. For example, it may increase the chances of survival for that particular animal, this is natural selection.

Example source: CGP

3.30 describe the process of evolution by means of natural selection

- Living things show variation
- The recourses living things need are limited. Individuals must compete for these resources to survive - only some will survive
- some of the varieties of a particular species will have a better chance of survival . Those varieties will have an increased chance of breeding and passing on their genes
- This means that a greater proportion of individuals in the next generation will have better alleles, and therefore better characteristics, that will help them to survive
- Over many generations, the species becomes better and better adapted to survive. The best features are naturally 'selected' and the species becomes more and more adapted to its environment.

Base notes: CGP

3.29 understand that a mutation is a rare, randon change in genetic material that can be inherited

A mutation is a rare, random change in an organism's DNA (basically, a mutation in a gene). This can be inherited. Mutations are often harmful as they change the sequence of the DNA bases. This could stop the production of a certain protein, or produce the wrong protein.

3.28 understand that variation within a species can be genetic, environmental or a combination of both

Genetic variation is just variation that you inherit, environmental variation is variation that is affected by your environment. That was a bit confusing, here are some examples to clear your mind...

Genetic variation
- Eye colour
- Natural hair colour
- Blood type
- Inherited disorders (e.g. haemophilia, cystic fibrosis)

environmental variation
- Non-inherited disorders (such as PTSD)
- Bad health (such as smoking) can lead to diseases such as cancer and heart disease

NOTE: Some characteristics are affected by genetic and environmental, such as growth. For example, a baby can be very small if the mother does not eat enough during pregnancy (environmental), having a poor diet can stunt your growth (environmental), but you could also just have a short family )
(genetic). Intelligence is also a mixture of both, whilst your maximum IQ is determined by your inheritance, factors such as your upbringing and school life affect how 'clever' you are. Sporting ability is determined by genes, but you also need to train, again it is a mixture of the two.

3.27 know that in human cells te diploid number of chromosomes is 46 and the haploid number is 23

Quite a simple one... in human cells, the diploid number of chromosomes is 46 and the haploid number is 23.

NOTE: All human cells are diploid (have 46 chromosomes) except gametes which are haploid (and have only 23 chromosomes).

3.25 understand that division of a cell by meiosis produces four cells, each with half the numberof chromosomes, and that this results in the formation of genetially different haploid cells

Gametes (sex cells) are produced by meiosis. Meiosis is when a cell reproduces by splitting itseld to form four haploid cells whose chromosomes are not identical. This is the process...


1- The cell duplicates its DNA (chromosomes) so there is enough DNA for each new cell

2- The chromosomes line up in pairs in the centre of the cell

3- The pairs cross over, some of the DNA from each chromosome is swapped. This means each new cell will have a mixture of the two original chromosomes.

4- The chromosomes are pulled apart and they form 2 separate cells

5- These cells are pulled apart, the arms of the chromosomes are pulled apart too (so there is one arm in each cell).

This results in four haploid gametes (haploid because they have half the number, only 23, of chromosomes rather than 46 as each cell has one arm of a chromosome). this means all four gametes are genetically different.

image source: vce.bioninja

3.24 understand that mitosis occurs in growth, repair, cloning and asexual reproduction

Mitosis is wen a cell reproduces itself by splitting to form two cells with identical sets of chromosomes. It is used for asexual reproduction, growth and repair of damaged cells, and cloning.

3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.

Okay so mitosis is when a cell reproduces by splitting itself in two to form two cells with identical sets of chromosomes (this is the definition we need for exams). This means that when a diploid cell (with 46 chromosomes) divides by mitosis, two diploid cells (both with identical 46 chromosomes) result. This is how it works...

NOTE: we do not need to learn the names of each stage for the exam, this is just the best diagram I could find :)

image source: publications.nigms.nih.gov
 

3.22 describe the determination of the sex of offspring at fertillisation, using a genetic diagram

This is a very good diagram which basically has everything on...



From this we can understand that there is a 50% chance of an offspring being male (XY) and a 50% chance of the offspring being female (XX).

image source: biologymad.com

3.21 understand that the sex of a person is controntrolled by one pair of chrmosomes, XX in a female and XY in a male

Firstly, it is important to understand that there are 23 pairs of chromosomes in each human cell, resulting is 46 individual chromosomes. (NOTE: there are only 23 chromosomes in sex cells, this is known as haploid). The 23rd pair is the one that determines whether you are male or female. Every male has 'XY' as his 23rd pair and every female has 'XX' as their 23rd pair. The female can only give X alleles, whilst the male can give X or Y alleles. This results in a combination of 2 XX genotypes and 2 XY genotypes, meaning there is a 50% chance of being male and a 50% chance of being female. This diagram may help for understanding...


image source: boiledpizza.blogspot

3.20 predict the probabilities of outcomes from monohybrid crosses

The each parent gives one allele to the offspring. There are two possible alleles it could give (for example, 'Bb' there is 'B' and 'b'). Therefore, if there are two parents, and each parent can give a possibility of one of two alleles, this means there are 4 possibilities overall for the offspring. I explained that so oddly, here is a diagram which will probably help more...



 

If you are asked to work out the probability of a child inheriting a genotype/phenotype, just count how many times it comes up and divide it by 4 (then x by 100 to get a %).

For example, if you are given the diagram above and asked to work out the probability the offspring will inherit 'Bb'. First you count how many 'Bb' are present, the answer is 2.Now divide 2 by 4 (this is because there are 4 possibilities) = 0.5. Now x0.5 by 100 to make a %. 0.5 x 100 = 50. So there is a 50% chance the offspring will inherit 'Bb'.

Image credit: scienceaid

3.19 understand hwo to interpret family pedigrees

A pedigree diagram enables someone to easily show a specific gene within a family. Here's how they work...

- A square represents a male
- A circle represents a female
- Coloured in represents the person has that allele/characteristic
- Blank implies that the characteristic/allele is not present
- You may see half a square/circle coloured in. This implies the allele is present but recessive so the characteristic is not present.

NOTE: This is not always the case but most often is, in an exam situation there will be a key so you do not need to learn this.


For example, in this particular family, the mother carries a particular gene, which the sons have inherited. However, the father and daughters do not carry this gene...

3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

Dominant - If an allele is dominant, the characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair. A dominant allele is always shown with capital letters. For example, 'BB'

Recessive - if the allele is recessive the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair. If there is only one recessive allele present, the characteristics of the dominant allele will show. A recessive allele is portrayed with lowercase letters. For example, 'ee'.

NOTE:  If you have two alleles, the version of the characteristic that appears will be dominant. For example, if you inherit one allele for brown eyes (BB) which is dominant and one allele for blue eyes (ee) which is recessive, the dominant characteristic will show, so you will have brown eyes. The only way you could have blue eyes is if you inherited two alleles for blue eyes. as this allele is recessive.

Homozygous - If you are homozygous, you have inherited two of the same alleles (e.g. BB or ee). All this means is that you have inherited, for example, two alleles for blue eyes or two alleles for brown eyes.

Heterozygous - If you are heterozygous, you have inherited two different alleles for that particular gene (e.g. Bb). All this means is you have most likely inherited one recessive and one dominant, in which case the characteristics of the dominant allele will show.

Phenotype - The phenotype is the characteristic that the alleles produce. For example, brown eyes, blonde hair, brown hair, blue eyes and so on.

Genotype - The genotype is the allele configuration you have inherited. For example, 'Bb', 'BB', 'ee' and so non.

Codominance - If you happen to inherit two dominant alleles, this is called codominance. This is where neither allele is recessive so you show characteristics from both alleles, as one is not dominant over the other. For example, blood group A is dominant and so is blood group B, so if you inherit an allele for A and an allele for B, you will end up with blood group AB.

3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics

Different forms of a gene are known as alleles. For example, for the gene that codes for eye colour there are alleles that code for brown eye colour and alleles that code for blue eye colour.