Photosynthesis

Question 1

What are chloroplasts?

Answer 1

Chloroplasts are small green organelles that contain a green pigment called chlorophyll.

Question 2

What happens during photosynthesis?

Answer 2

Light energy is absorbed by chlorophyll( in chloroplasts). This energy is used to convert carbon dioxide from the air and water from the soil into glucose and oxygen
- Photosynthesis happens in all green plants and algae.

Question 3

What is the test for starch?

Answer 3

Iodine solution is a yellowy-brown liquid. It turns dark blue when it reacts with starch. You can use this to test for starch, to show photosynthesis has taken place( a lot of glucose made in Photo-S is converted into insoluble starch and stored).

Extra: you need to treat leaves by boiling them in ethanol, to remove the waterproof cuticle and remove the colour, as iodine can’t react with starch with waterproof cuticle and chlorophyll masks colour change.

Question 4

How are leaves adapted for photosynthesis?( absorbing light)

Answer 4

• Most leaves are broad, giving them a big surface area for light to fall on.
• Leaves contain lots of chloroplasts. Chloroplasts contain chlorophyll to absorb light energy from sun.
• The cells that contain the most chloroplasts are arranged in a palisade layer near the top of the leaf where they can get the most light.
• The upper epidermis is transparent so that light can pass through it to the palisade layer.

Question 5

How are algae adapted for photosynthesis ?

Answer 5

Absorb carbon dioxide dissolved in water around them.

Question 6

How does light affect photosynthesis?

Answer 6

As light intensity increases, so does the rate of photosynthesis. This is because light is a raw material in photosynthesis and provides energy for the process. If this was in graph form, the graph has an increasing gradient until it reaches a peak at a certain point, then it levels off, showing that light is no longer a limiting factor.

Question 7

How does carbon dioxide affect the rate of photosynthesis?

Answer 7

Because Carbon dioxide is one of the raw materials in photosynthesis. As CO2 levels increase, the rate of photosynthesis also increased steadily- but only up to a certain point. Beyond that, it won’t make any difference, it’ll be either the temperature or light intensity that will be limiting.
In graph form we see the graph flattens out, showing that CO2 is no longer a limiting factor.

Question 8

How can you change light intensity in a lab?

Answer 8

By moving a lamp closer or further away from a plant. But you can’t plot the rate of photosynthesis against “distance of lamp from the beaker” or you get a weirdly shaped graph. You need to measure the light intensity at the beaker using a light meter.

Question 9

How can you control the amount of co2?

Answer 9

Dissolve different amounts of sodium hydrogencarbonate in the water, which gives off CO2

Question 10

What is the word equation of photosynthesis?

Answer 10

Carbon dioxide + water= glucose + oxygen

Question 11

How does temperature affect the rate of photosynthesis?

Answer 11

If temperature is a limiting factor it’s because it’s too low- enzymes needed for photosynthesis work more slowly at low temperatures.

Normally as temperature increases, so does the rate of photosynthesis, until about 45 degrees(when the plant gets too hot) , then the enzymes needed for photosynthesis denature. The rate of photosynthesis falls.

Question 12

How does water vapour leave cells?

Answer 12

The water vapour evaporates from the cells inside the leaf. Then it escapes by diffusion because there’s a lot of it inside the leaf and less of it in the air outside.
Evaporation is quickest in hot, dry, windy conditions.

Question 13

How can you conduct experiments for the ideal conditions for photosynthesis?

Answer 13

Use a Canadian pondweed- you can easily measure the amount of oxygen produced in a given time to show how fast photosynthesis is happening(as oxygen is made during photosynthesis).
You could either count the bubbles given off, or for accuracy, you could collect the oxygen in a gas syringe.

In experiments such as these, you need to keep all variables constant apart from that you’re investigating, so it’s a fair test.

• use a bench lamp to control light intensity( and don’t block light with anything).
• keep flask in water bath to keep temperature constant
• for co2, can’t do much- you just have to use a large flask and do experiments as quickly as you can so that the plant doesn’t use too much of the CO2 in the flask.

Question 14

How do plants use glucose?

Answer 14

For RESPIRATION. This releases energy which enables them to convert the rest of the glucose into other useful substances, which they can use to build new cells and grow. It builds up small molecules into bigger ones.
MAKING PROTEINS. Glucose is combined with nitrate ions to make amino acids, which are then made into proteins.
MAKING CELL WALLS: Glucose converted into cellulose for making strong cell walls.
STORED as STARCH: Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn’t happening, like in winter.
Potato and parsnip store a lot of starch underground over the winter so a new plant can grow from it the following spring.
STORED in SEEDS. Glucose is turned into lipids( fats and oils) for storing in seeds. Can use to get cooking oil.

Question 15

Why is starch much better at storing than glucose?

Answer 15

Starch is insoluble but glucose is soluble.
Lots of glucose in cells would affect osmosis inside cells, it would draw loads of water into the cell and the cell would swell up.

Question 16

What is the function of a greenhouse? And how do they artificially create ideal conditions for farming?

Answer 16

Greenhouses help to trap the sun’s heat and make sure that temperature doesn’t become limiting.
In winter farmers might use a heater as well to keep the temperature at the ideal level. In summer it could get too hot, do they might use shades and ventilation to cool things down.
Light is always needed in photosynthesis, so commercial farmers often supply artificial light after the sun goes down to give plants more quality photosynthesis time.
Farmers and gardeners might also increase CO2 levels by using a paraffin heater to heat the greenhouse. As the paraffin burns, it makes carbon dioxide as a byproduct.

Question 17

What are the advantages and disadvantages of greenhouses?

Answer 17

Keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases. The farmer can also add fertilisers to the soil as well, to provide all the nutrients needed for healthy growth.
Increases yields, as plantsgrow faster if farmer can keep conditions just right for photosynthesis
Grow things in climates where it wouldn’t be possible.

Costs money
Takes a lot of energy to control conditions in greenhouse… Fossil fuels…

Question 18

Why would plant leaves be yellow?

Answer 18

Lack magnesium, magnesium makes chlorophyll for photosynthesis

Question 19

What are mineral ions, potassium and nitrates used for?

Answer 19

Potassium is good for flowers, fruit and disease resistance.
Mineral ions are needed for healthy growth
Nitrates help with growing and making proteins

Question 20

Which are the limiting factors during night and winter?

Answer 20

At night, light is limiting

Winter, temperature is limiting

Question 21

Why is co2 limiting on a sunny day?

Answer 21

Both bright and warm enough. Carbon dioxide levels tend to rise at night. Because in the dark, plants don’t photosynthesise but they can respire. As temp and light increases in morning, all co2 is used up.

Question 22

How are plants adapted for photosynthesis( diffusion)?

Answer 22

• They contain air spaces, which allow carbon dioxide diffuse into the cells and oxygen to leave by diffusion.
• The underneath of the leaf is an exchange surface. It’s covered in tiny openings called stomata, which CO2 diffuses in through and oxygen and water vapour out.
• The size of the stomata are controlled by guard cells. These close the stomata if the plant is losing water faster than it’s being replaced in roots. Without guard cells the plant would soon wilt.
• The flattened shape of the leaf increases the area of this exchange, so more effective
• The walls of the cells inside the lead form another exchange surface. The air spaces inside the leaf increase the area of this surface so there’s more chance for carbon dioxide to get into the cells.
• Have a network of vascular bundles( the transport vessels, xylem and phloem).