Nutrition in flowering plants

Question 1

What is photosynthesis?

Answer 1

The process of converting light energy to chemical energy, which is stored as glucose (the food of the plant)

Question 2

Where does photosynthesis take place?

Answer 2

In the leaves of all green plants (inside the chloroplasts)

Question 3

What do chloroplasts contain?

Answer 3

A pigment called chlorophyll which absorbs sunlight and uses the energy to convert carbon dioxide and water into glucose. Oxygen is also produced

Question 4

What is the word and chemical equation for photosynthesis?

Answer 4

Word equation:
carbon dioxide + water —> glucose + oxygen

Chemical equation:
6CO2 + 6H2O + —> C6H12O6 + 6O2

Question 5

What have been designed for making food in photosynthesis efficient?

Answer 5

Leaves

Question 6

How have leaves adapted for photosynthesis?

Answer 6

• Broad leaves - large sa exposed to light
• Chloroplasts found in palisade layer - near the top so get the most light
• Upper epidermis is transparent - light can pass through
• Network of vascular bundles (xylen and phloem) - support leaf structure + deliver water and nutrients around leaf and get rid of glucose
• Waxy cuticles reduce water loss by evaporation
• Have small holes called stomata - let CO2 diffuse directly into the leaf

Question 7

What are limiting factors?

Answer 7

Something which stops photosynthesis from happening any faster

Question 8

What are the limiting factors of photosynthesis?

Answer 8

• Light intensity
• CO2 concentration
• Temperature

Question 9

What do limiting factors depend on?

Answer 9

The environmental conditions eg in winter low temperatures might be a limiting factor or at night, light might be a limiting factor

Question 10

What happens if there is not enough light?

Answer 10

The rate of photosynthesis is slowed down

Question 11

Describe what happens as light intensity increases?

Answer 11

• The rate of photosynthesis increases steadily but only until a certain point.
• Beyond that point it wont make any difference because temperature and CO2 conc will now be the limiting factor

Question 12

What happens if the there is too little carbon dioxides?

Answer 12

The rate of photosynthesis is slowed down

Question 13

Describe what happens as carbon dioxide increases

Answer 13

• Increasing the concentration of carbon dioxide increases the rate of photosynthesis up to a certain point
• CO2 is then no longer a limiting factor and as long as that and light are in plentiful supply, the only limiting factor left is temperature

Question 14

Why does temperature affect the rate of photosynthesis?

Answer 14

It affects the enzymes involved in photosynthesis

Question 15

Describe what happens as the temperature increases?

Answer 15

• As the temperature increases, so does the rate of photosynthesis up to a certain point
• If the temperature is too high (above 45) the plants enzymes will be denatured so the rate decreases

Usually if the temperature is the limiting factor, its because its too low and needs warming up

Question 16

Why do you test for starch and oxygen to investigate photosynthesis?

Answer 16

The two products from photosynthesis are glucose and oxygen and glucose is stored by plants as starch.

Question 17

How can you test a leaf for starch? (Describe experiment)

Answer 17

• Kill leaf by dunking in boiling water (stops chemical reactions taking place)
• Put leaf in ethanol and heat in tube in water bath (gets ride of chlorophyll leaving the leaf a white-ish colour)
• Rinse leaf in cold water and add a few drops of iodine

If starch is present leaf inside turns blue-black

Question 18

Why does starch show whether photosynthesis is taking place?

Answer 18

Because if a plant cannot photosynthesise, it cannot make starch

Question 19

Describe an experiment to show that chlorophyll is needed for photosynthesis

Answer 19

• Take a variegated (green and white) and expose it to light
• Test the leaf for starch using iodine solution (only the green bits will turn blue-black)

Question 20

What does the variegated cell suggest about chlorophyll and photosynthesis?

Answer 20

Only the parts of the leaf that contain chlorophyll (green) are able to photosynthesise and produce starch

Question 21

Describe an experiment to show CO2 is needed in photosynthesis?

Answer 21

• Put inside a sealed jar a plant and soda lime. Shine a light over them
• The soda lime will absorb CO2 out of the air in the jar
• If you leave the plant in the jar for a while and test for starch it wont turn blue-black

This shows that no starch has been made which means that CO2 is needed

Question 22

Describe an experiment to show that light is needed for photosynthesis

Answer 22

• Use a plant that has been grown without any light eg in a cupboard
• Cut a leaf from the plant and test it for starch (using iodine solution). The leaf will not turn blue-black
• This shows that light is needed as no starch is needed

Question 23

What shows the rate of photosynthesis?

Answer 23

Oxygen production

Question 24

What can be used to show the rate of photosynthesis (oxygen production)

Answer 24

Canadian pondweed - the rate at which the pondweed produces oxygen corresponds to the rate of photosynthesis (the faster the rate of oxygen the faster the rate of photosynthesis)

Question 25

Describe an experiment to show oxygen production using Canadian weed

Answer 25

• A source of white light is placed a specific distance away from the test tube of Canadian weed
• The pondweed is left to photosynthesise for a certain amount of time (oxygen released in capillary tube)
• A syringe is used to draw the gas bubble in the tube alongside a ruler so it cab measured (proportional to the volume of oxygen produced)
• The experiment is repeated with the light source at different distances away from the pondweed

Question 26

In the experiment to show oxygen production using Canadian weed, what variables should be controlled?

Answer 26

• Temperature

- Time pondweed left to photosynthesise

Question 27

How can the experiment to show oxygen production using Canadian weed be altered to show how temperature and CO2 affect photosynthesis?

Answer 27

Temperature - Put test tube of pondweed into a beaker of water at a set temperature

CO2 - Bubble through test tube