2.49 Understand why simple, unicellular organisms can rely on diffusion for
movement of substances in and out of the cell.
- Unicellular organisms (including fungi and bacteria) have a large surface area to volume ratio
- Are small and so the diffusion distance is short, meaning diffusion happens very quickly.
2.50 Understand the need for a transport system in multicellular organisms.
- Multicellular organisms have Small surface area to volume ratio
- The diffusion distance would be very large and so very slow.
- This wouldn't support the organism; so they have developed transport systems, like the ventilation system and the circulatory system which speed up the process of getting necessary molecules in and out of the body enough to support themselves.
Flowering Plants
2.52 Describe the role of xylem in transporting water and mineral salts from the roots to other parts of the plant.
2.53 Explain how water is absorbed by root hair cells.
- Roots branch to increase the surface area and to increase the chances of finding a water source.
- Root hairs are epidermal cells on the surface of the root:
- They also increase the surface area for absorption.
- They absorb minerals by active transport and water by osmosis.
- These substances then move to the xylem.
2.54 Understand that transpiration is the evaporation of water from the surface of a plant.
Transpiration: The process where water is absorbed through the roots of a plant, which then later water evaporates through the pores in their leaves.
- Heat from sunlight is absorbed into the leaf
- This turns the liquid water into gas (steam).
- This gas then evaporates through the stomata, out of the leaf.
2.55 Explain how the rate of transpiration is affected by changes in the following factors:
Humidity
Light intensity
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Wind speed
Temperature
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2.56 Describe experiments to investigate the role of environmental factors in
determining the rate of transpiration from a leafy shoot.
- Support a plant in a tray filled with a given amount of water.
- Place in different conditions and record the time taken for all the water in the way to be taken up by the plant.
Humans
2.57 Describe the composition of the blood: red blood cells, white blood cells,platelets and plasma.
The blood has several different components:
- 55% of the blood is plasma: yellow liquid containing water with different things dissolved in it.
- There are many red blood cells (Erythroeytes.)
- There are less white cells: Phagosytes; lymphosytes.
- Platelets (dead red blood cells) which play an important role in clotting.
2.58 Understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy.
Water is the main component of plasma is a solvent and a liquid; so plasma carries different things around the body.
The following things are dissolved in water and carried around the body:
The following things are dissolved in water and carried around the body:
- Carbon (Hydrogen carbonate),
- Digested food (soluble sugars and amino acids),
- Urea,
- Hormones.
2.59 Explain how adaptations of red blood cells, including shape, structure and
the presence of haemoglobin, make them suitable for the transport of oxygen.
- Red blood cells carry oxygen around the body.
- In order to do this they have haemoglobin (which is made from iron) that can bond to oxygen.
- Red blood cells have no nucleus which makes more room for the haemoglobin.
- There are no mitochondria as the cells respire anaerobically so the cells don't use any oxygen.
- They are biconcave; they are a flat disk with a dip in the middle.
- The shape of a flat disk enables them to pass through narrow capillaries .
- They have a dip in the middle to increase the surface area
- This decreases the distance for diffusion meaning that diffusion of oxygen happens quickly.
- The shape of a flat disk enables them to pass through narrow capillaries .
2.60 Describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogen.
White blood cells are specialised cells which can stop pathogens in your body.
Phagocytes
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Lymphocytes
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2.63 Describe the structure of the heart and how it functions.
The heart can be thought of in four sections:
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A description of the workings of the heart:
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2.64 Explain how the heart rate changes during exercise and under the influence of adrenaline.
- During exercise muscles require more energy which is released by respiration
- This means more oxygen is required to be brought to cells and more carbon dioxide to be taken away.
- Therefore the heart needs to increase its speed so that more blood is sent to muscles.
- Adrenalin stimulates adrenergic receptors in the heart which increase the rate that your heart cells work at.
2.65 Describe the structure of arteries, veins and capillaries and understand their roles.
Arteries
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Veins
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Capillaries
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