Biology Topic 3

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What is the word equation for photosynthesis?
carbon dioxide + water ------ w/ sunlgiht+chlorophyll ---> glucose + oxyg
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What is the chemical equation for photosynthesis?
6CO2 + 6H20 -> C6H12O6 + 6O2
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How are leaves designed for photosynthesis?
Waxy cuticle, upper epidermis, chloroplasts, vascular bundle, guard cells, stoma, air space, palisade and spongy mesophyll layer.
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How are leaves adapted for efficient photosynthesis?
Leaves are broad- large surface area. Chloroplasts found in palisade layer - near top of leaf, get most light. Upper epidermis is transparent- light pass through to palisade layer. VBs- deliver water+nutrients to all of leaf + remove glucose,support.
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How are leaves adapted for efficient photosynthesis? (2)
Waxy cuticle- reduce water loss by evaporation. Efficient gas exchange through stomata.
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What is a limiting factor?
Something which stops photosynthesis from happening any faster. They depend on the environmental conditions. EG, light intensity, CO2, concentration and temperature.
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What happens if there is not enough light?
The rate of photosynthesis decreases.
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What happens if there is too little carbon dioxide?
The rate of photosynthesis decreases.
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What effect does the temperature have?
If the temperature increases, it reaches an optimum until it gets too high and the enzymes denature.
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How do you test a leaf for starch?
Dunk a leaf in boiling water, holding it with tweezers, then place in a boiling tube with ethanol and heat the tube in a water bath (removing chlorophyll inside the leaf), rinse the leaf in cold water, add iodine solution. Starch = blue-black.
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What does the starch test show?
Whether photosynthesis is taking place. If a plant can't photosynthesise it can't make starch.
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How to show that chlorophyll is needed for photosynthesis using variegated leaves.
Take a variegated leaf from a plant that's been exposed to light for a bit, recording which bits are white and which are green. Test for starch. Bits that were green turn blue-black, showing places of the leaf containing chlorophyll photosynthesise.
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How to show that CO2 is needed for photosynthesis.
Soda lime will absorb CO2 out of the air in the jar, leave the plant in the jar for a while and then test for starch. It won't turn blue-black, no starch has been made, showing CO2 is needed for photosynthesis.
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How to show that light is needed for photosynthesis.
Grow a plant in an environment with no light. Cut a leaf from the plant and test for starch. The leaf won't turn blue-black, showing light is needed.
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How to show the oxygen production slows the rate of photosynthesis.
Canadian pondweed can measure the effect of light intensity on the rate of photosynthesis. A source of white light is placed at a specific distance from pondweed, left for a set amount of time. Oxygen released is collected in a capillary tube.
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How to show the oxygen production slows the rate of photosynthesis. (Part 2)
At the end of the experiment, the syringe draws the gas bubble in the tube up alongside a ruler. Length of gas bubble measured, proportional to volume of O2.
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What three main mineral ions are needed for plant growth?
Nitrates (making amino acids+proteins, cell growth- lack = stunting+yellow leaves), Phosphates (make DNA+membranes, respiration+growth, lack=purple leaves+poor root growth), Potassium (enzymes needed, lack= poor growth, discoloured leaves).
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Why is magnesium needed in small amounts for growth?
Required to make chlorophyll, needed for photosynthesis. Without it, plants have yellow leaves.
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Why do multicellular organisms need transport systems?
Cells in living organisms need a variety of substances to live, eg water, minerals and sugars. They also need to get rid of waste substances. Unicellular- substances diffuse directly, quick because of short distance. Multicellular-too slow,need this.
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What are the two main transport systems for plants?
Xylem tubes - transport water and minerals- carry up from the roots via the shoot to the leaves. Phloem tubes - food - sucrose, amino acids from leaves to other parts - TRANSLOCATION.
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What is the job of root hairs?
To take in water. The cells on plant roots grow long hairs sticking into the soil, each branch is covered in millions of these, giving a bigger surface area for absorbing water from the soil via osmosis.
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What is transpiration?
The loss of water from the plant. It is a side-effect of the way leaves are adapted for photosynthesis. Stomata, gas exchange- more water in plant than in air outside, diffuse quickly.
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How does transpiration work?
Evaporation and diffusion of water from a plan't surface (leaves mainly). Evaporation causes slight shortage of water, more drawn up through xylem vessels. More water from roots, constant transpiration stream of water through the plant.
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How does the light intensity affect the transpiration rate?
Brighter light = greater rate. Stomata close as it gets darker, photosynthesis can't happen in the dark don't open for CO2, very little water can escape.
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How does the temperature affect the transpiration rate?
Warmer = faster rate. Water particles have more energy to evaporate and diffuse out of the stomata.
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How does the wind speed affect the transpiration rate?
Higher wind speed = greater rate. Low wind speed, water surrounds leaf and doesn't move away- high concentration both areas so no diffusion. Water swept away, low concentration outside- diffusion is quicker.
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How does the humidity affect the transpiration rate?
Drier air around leaf = faster rate. If the air is humid, there's a lot of water in it already. Diffusion is fastest at a really high and really low concentration.
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How do you measure transpiration?
Potometer can estimate the transpiration rate. It measures the water uptake by a plant, but its assumed the water uptake is directly related to water loss by the leaves.
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How does a potometer work?
Cut shoot underwater at slant (increase the surface area),prevent air entering the xylem. Assemble in water, remove apparatus but keep capillary tube submerged in beaker of water. Watertight+airtight. Dry leaves, shoot acclimatise, shut tap.
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How does a potometer work? (2)
Remove the end of capillary tube until one air bubble formed, then place back into the water. Record starting position- stopwatch, distance moved by the bubble per unit time.
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How does light intensity affect transpiration rates?
Use a lamp to increase the intensity of light hitting the plant- should increase the rate. Decrease, by placing potometer in cupboard, decrease rate.
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How does temperature affect transpiration rates?
Increase or decrease it by placing potometer in a room that's colder or warmer than control experiment. Increase in temperature = increase in rate.
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How does the humidity affect transpiration rates?
Increase the humidity of the air around the plant by spraying water into a clear plastic bag before sealing it around the plant. Decreases the rate.
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How does the wind speed affect transpiration rates?
Use a fan to increase the wind speed around the plant, increases the rate.
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Card 2

Front

What is the chemical equation for photosynthesis?

Back

6CO2 + 6H20 -> C6H12O6 + 6O2

Card 3

Front

How are leaves designed for photosynthesis?

Back

Preview of the front of card 3

Card 4

Front

How are leaves adapted for efficient photosynthesis?

Back

Preview of the front of card 4

Card 5

Front

How are leaves adapted for efficient photosynthesis? (2)

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Preview of the front of card 5
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