GCSE Biology 2a

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• Cells

1. Animal Cell
   1. Nucleus
      2. Contains genetic material that controls the activities of the cell
   2. Cytoplasm
      2. Gel-like substance where most of the chemical reactions happen. It contains enzymes that control most of the chemical reactions.
   3. Ribosomes
      2. These are where proteins are made in the cell
   4. Mitrochondria
      2. These are where most of the reactions for respiration take place. Respiration releases the energy that is needed for the cell to work.
   5. Cell Membrane
      2. Holds the cell together and controls what goes in and out
2. Bacterial Cell
   1. A bacterial cell has cytoplasm and a cell membrane surrounded my a cell wall
   2. The genetic material floats in the cytoplasm because bacteria don't have a nucleus.
3. Yeast Cell
   1. A yeast cell has a nucleus, cytoplasm, and a cell membrane surrounded by a cell wall
4. Plant Cell
   1. Cell Wall
      1. Made of Cellulose. It supports the cell and strengthens it.
   2. Permanent Vacuole
      1. Contains cell sap, a weak solution of sugar and salts
   3. Chloroplasts
      1. This is where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll.

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• Diffusion

1. Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration
2. Diffusion happens in both solutions and gases - this is because the particles in these substances are free to move about randomly.
3. The bigger the difference in concentration, the faster the diffusion rate
4. Cell Membranes
   1. They are quite clever because they hold the cell together but they let stuff in and out as well
   2. Dissolved substances can move in and out by diffusion
   3. Big molecules like starch and proteins can't fit through the membrane.
   4. only very small molecules can diffuse through cell membranes
   5. Just like with diffusion in air, particles flow through the cell membrane from where there's a high concentration to where there is a low concentration
   6. The particles only move about randomly so they can go both ways, but if there are a lot more particles on one side of the membrane then there is a net (overall) movement from that side.

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• Specialised Cells

1. Palisade Leaf Cells
   1. They are adapted for photosynthesis
   2. Packed with chloroplasts for photosynthesis. more of them are crammed on the top of the cell - so they are closer to the light
   3. Tall shape means a lot of surface area exposed down the side for absorbing CO2 from the air in the leaf.
   4. Thin shape means that you can pack loads of them in at the top of a leaf.
2. Guard Cells
   1. They are adapted to open and close pores
   2. Special kidney shape which opens and closes the stomata (pores) in the leaf
   3. When the plant has lots of water the guard cells fill with it and go plump and turgid, this makes the stomata open so gases can be exchanged for photosynthesis
   4. When the plant is short of water, the guard cells lose water and become flaccid, making the stomata close. This helps to stop too much water vapor from excaping
   5. Thin outer walls and thickened inner walls make the opening and closing work.
   6. They're also sensitive to light and close at night to save water without loosing out on photosynthesis.
   7. Guard cells are adapted to their function of allowing gas exchange and controlling water loss within the leaf.
3. Red Blood Cells
   1. They are adapted to carry oxygen
   2. Their concave shape gives a big surface area for absorbing oxygen. It also helps them pass smoothly through capillaries to reach body cells.
   3. They are packed with haemoglobin - the pigment that absorbs the oxygen.
   4. They have no nucleus, to leave more room for heloglobin.
4. Sperm and Egg Cells
   1. They are specialised for reproducton and are very important.
   2. The main function of an egg cell are to carry the female DNA and to nourish the developing embryo in the early stages. The egg cell contains huge food reserves to feed the embryo.
   3. When the sperm fuses with the egg, the egg's membrane instantly changes its structure to stop anymore sperm from getting in. This makes sure the offspring ends up with the right amount of DNA.
   4. The function of the sperm is basically to get the male DNA to the female DNA. It has a long tale and a streamline head to help it swim to the egg. There are a lot of mitochondria in the cell to provide the energy needed.
   5. Sperm also carry enzymes in their head to digest through the egg cell membrane.

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• Cell Organisation

1. 1) Large Multicellular Organisms Are Made Up Of Organ Systems.
   1. The process by which cells become specialised for a particular job is called differentation.
   2. Differentiation occours during the development of a multicellular organism.
   3. These specialised cells form tissues, which form organs, which form organ systems.
   4. Large multicellular organisms have different systems inside them for exchanging and transporting materials
2. 2) Similar Cells Are Organised Into Tissues
   1. A tissue is a group of similar cells that work together to carry out a particular function. It can include more than one type of cell. in mammals examples of tissues include:
      1. Muscular tissue. which contracts (shortens) to move whatever it is attached to.
      2. Glandular tissue, which makes and secretes chemicals like enzymes and hormones
      3. Epithelial tissue, which covers part of the body, e.g. the inside of the gut.
3. 3) Tissues Are Organised Into Organs.
   1. An organ is a group of different tissues that work together to perform a certain function, For example the stomach organ is made out of tissues:
      1. Muscular tissue, which moves the stomach wall to churn up the food.
      2. Glandular tissue, which makes digestive juices to digest food.
      3. Epithelial tissue, which covers the inside and outside of the stomach.
4. 4) Organs Are Organised Into Organ Systems.
   1. An organ system is a group of organs that are working together to perform a particular function, for example, the digestive system breaks down food and is make out of these organs:
      1. Glands (e.g. the pancreas and salivary glands), which produce digestive juices.
      2. The stomach and the small intestine, which digest food.
      3. The small intestine, which absorbs soluble food molecules.
      4. The large intestine, which absorbs water from undigested food, leaving faeces.
      5. The Digestive system exchanges materials with the environment by taking nutrients and releasing substances such as bile.

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• Plant structure and photosynthesis

1. Plant Cells Are Organised Into Tissues And Organs
   1. Plants are made of organs like stems, roots and leaves. These organs are made of tissues. For example leaves are made of:
      1. Mesophyll tissue - this is where most of the photosynthesis in a plant occurs.
      2. Xylem and phoem - they transport things like mater, mineral irons and sucrose around the plant.
      3. Epidermal tissue - this covers the whole plant.
2. Photosynthesis Equation
3. Photosynthesis produces glucose using sunlight
   1. Photosynthesis is the process that produces 'food' in plants and algae. the 'food' it produces is glucose.
   2. Photosynthesis happens inside the chloroplast.
   3. Chloroplast contains a green substance called chlorophyll, which absorbs sunlight and uses its energy to convert carbon dioxide (from the air) and water (from the soil) into glucose. Oxygen is also produced as a by-product.
   4. Photosynthesis happens in the leaves of all green plants - this is largely what the leaves are for,
   5. The cross section of a leaf showing the four raw materials needed for photosynthesis.

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• The Rate of Photosynthesis.

1. Photosynthesis Equation
2. The rate of photosynthesis is affected by the intensity of light, the volume of CO2, and the temperature. Plants also need water for photosynthesis, but when a plant is short of water it becomes the limiting factor in photosynthesis, its already in such trouble that this is the least of its worries.
3. The Limiting Factor Depends On Conditions
   1. Any three factors that affect photosynthesis can become a limiting factor. This just means that it's stopping photosynthesis from happening any faster.
   2. Which factor is limiting at a particular time depends on the environmental conditions:
      1. At night it's pretty obvious that light is the limiting factor.
      2. In water it's often the temperature.
      3. If it's warm enough and bright enough, the amount of CO2 is usually limited.
4. Three Important Graphs For Rate Of Photosynthesis
   1. Not Enough Light Slows Down Photosynthesis
      1. Light provides the energy needed for photosynthesis
      2. As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point.
      3. Beyond that, it wouldn't make any difference because then it'll be either the temperature or the CO2 level which will be the limiting factor.
      5. In the lab you can change the light intensity by moving a lamp closer to or further away from the plant.
      6. But if you just plot the rate of photosynthesis against "distance of light from the beaker" you get a weird shaped graph. To get the ideal graph you either need to measure the light intensity at the beaker using a light meter or do a bit of nifty maths with your results.
   2. Too Little Carbon Dioxide
      1. CO2 is one of the raw materials needed for photosynthesis
      3. As with light intensity the amount of CO2 will only increase the amount of photosynthesis up to a point. After this the graph flattens out showing that CO2 is no longer the limiting factor.
      4. As long as light and CO2 are in plentiful supply then the factor limiting photosynthesis must be temperature.
      5. There are lots of different ways to control the amount of CO2. one way is to dissolve different amounts of sodium hydrogencarbonate in the water which gives off CO2.
   3. The Temperature Has To Be Just Right
      1. Usually, if the temperature is the limiting factor it's because it's too low - the enzymes needed for photosynthesis work slower at low temperatures.
      2. But if the plant gets too hot, the enzymes will get damaged or denatured.
      3. Enzymes often get damaged at about 45°C
      5. Experimentally, the best way to control the temperature of a flask is to put it in a water bath.
5. You Can Artificially Create The Ideal Conditions For Farming
   1. The most common way to artificially create the ideal environment for plants is to grow them in a green house.
   2. Greenhouses help to trap the sun's heat, and make sure that the temperature doesn't become limiting. In winter a farmer or gardener might use a heater as well to keep the temperature at the ideal level. In the summer it could get too hot, so they might use shades and ventilation to cool things down.
   3. Light is always needed for photosynthesis, so commercial farmers often supply artificial light after the sun goes down to give their plants more quality photosynthesis time
   4. Farmers and gardeners can also increase the level of CO2 in the greenhouse. A fairly common was is to use a paraffin heater to heat the greenhouse. As the paraffin burns it makes CO2 as a by-product.
   5. Keeping plants enclosed in a greenhouse also makes it easier to keep it free from pests and diseases. The farmer can also add fertilisers to the soil as well, to provide all the minerals needed for healthy growth.
   6. Sorting all this out costs money - but if the farmer can keep the conditions just right for photosynthesis. the plants will row much faster and a decent crop can be harvested much more often, which can then be sold. It's important that the farmer supplies the right amount of heat, light, etc. - enough to make the plants grow well, but not more than the plant needs, as that would be wasting money.

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• How Plants Use Glucose

1. For Respiration
   1. 1) Plants manufacture glucose in their leaves.
   2. 2) They then use some of the glucose for respiration.
   3. 3) This releases energy which enables them to convert the rest of the glucose into various other useful substances, which they can use to build new cells and grow.
   4. To produce so,me of the other substances they also need to gather a few minerals from the soil.
2. Making New Cells
   1. Glucose is converted into cellulose for making strong cell walls, especially in a rapidly growing plant.
3. Making Proteins
   1. Glucose is combined with nitrate ions to make amino acids, which are them made into proteins.
4. Stored In Seeds
   1. Glucose is turned into lipids for storing in seeds, Sunflower seeds for example, contain a lot of oil- we get cooking oil and margarine from them. Seeds also store starch
5. Stored As Starch
   1. Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn't happening. like in winter. Starch is insoluble which makes it much better for storing than glucose - a cell with lots of glucose in would draw lots of water and swell up.

1. Organisms live in different places because the environment varies
   1. A habitat is a place where an organism lives, e.g. a playing field.
   2. The distribution of an organism is where an organism is found, e.g. in a part of the playing field.
   3. Where an organism is found is affected by environmental factors such as:
      1. Temperature
      2. Water available
      3. Oxygen and carbon dioxide available
      4. nutrients available
      5. Amount of light available
   4. An organism might be more common in one area than another due to differences in environmental factors between the two areas. For example, in a field, you might find that daisies are more common in in the open, than under trees, because there is more light available in the open.
   5. There are a couple of ways to study the distribution of an organism. you can:
      1. Measure how common an organism is in two sample areas (e.g. using quadrats) and compare them.
      2. Study how the distribution changes across an area e.g. by placing quadrats along a transect.
2. Use Quadrats To Study The Distribution Of Small Organisms.
   1. A quadrat is a square frame enclosing a known area, e.g. 1m². to compare how common an organism is in two sample areas.
   2. 1) place a 1m² quadrat on the ground at a random point within the first sample area.
   3. 2) count all the organisms within the quadrat.
   4. 3) Repeat stops 1 and 2 as many times as possible.
   5. 4) Work out the mean number of organisms per quadrat within the first sample area.
   6. 5) Repeat steps 1-4 in the second sample area.
   7. 6) finally compare the two means. E.g. you might find 2 daisies per m² in the shade, and 22 daisies per m² in the open field.
3. Working Out Population Size.
   1. 1) Work out the mean number of organisms per m²
   2. 2) Then multiply the mean by the total area (in m²) of the habitat.
      1. E.g. if the area of an open field is 800 m², and there are 22 daisies per m², then the size of the daisy population is 22 X 800 = 17,600
4. Use Transects to study the distribution of organisms along a line.
   1. You can use lines called transects to help find out how organisms are distributed across an ares - e.g. if an organism because more or less common as you move from hedge towards the middle of a field.
   2. How
      1. 1) Mark out a line in the area you want to study using a tape measure.
      2. 2) Then collect data along the line.
      3. 3) You can do this by just counting all the organisms that you're interested in that touch the line.
      4. 4) Or you could collect data by using quadrats. These can be placed next to each other along the line or at intervals, for example, every 2 m.
5. When Collecting Environmental Data You Need To Think About...
   1. Reliability
      1. 1) Quadrats and transects are pretty good tools for finding out how an organism is distributed.
      2. 2) But you have to work hard to make sure that your results are reliable - which means making sure they are reproducible and repeatable.
      3. 3) To make your results more reliable you need to take a large sample size, e.g. use as many quadrats and transects as possible in your sample area. Bigger samples are more representative of the whole population.
   2. Validity
      1. 1) For your results to be valid they must be reliable and answer the original question.
      2. 2) to answer the original question, you need to control all the variables.
      3. 3) The question you want to answer is whether a difference in distribution between two sample areas is due to a difference in the environmental factor.
      4. 4) If you've controlled all the other variables that could be affecting the distribution, you'll know whether a difference in distribution is caused by an environmental factor or not.
      5. 5) IF you don't control the other variables you won't know whether any correlation you've found is because of chance, because of the environmental factor you're looking at or because of a different variable - the study won't give any valid data.
      6. 6) Use random samples, e.g. randomly put down or mark out your quadrat or transect. If all your samples are in one spot, and everywhere else is different, the results you get wouldn't be valid.