2. Organisation (photosynthesis and adaptations of a leaf)

Question 1

What is the word equation for photosynthesis?

Answer 1

carbon dioxide + water —–> glucose + oxygen

Question 2

What is the chemical equation for photsynthesis?

Answer 2

6CO2 + 6H2O —–> C6H12O6 + 6O2

Question 3

What is glucose converted into to be stored?

Answer 3

Starch

Question 4

Why is glucose converted into starch?

Answer 4

• Starch is insoluble so doesn’t affect osmotic pressure
• Starch is branched, so more compact, and can be stored more easily

Question 5

When is water potential highest?

Answer 5

For pure water, where no other solutes are dissolved in it

Question 6

What happens to water potential if solutes are added to pure water?

Answer 6

It gets more negative

Question 7

What happens if glucose is not converted into starch to be stored?

Answer 7

• If glucose isn’t converted into starch to be stored
• it will dissolve in the water inside the cells of the plant
• so this will make the water potential more negative than the water potential outside the cells
• so water will start to move into the cells
• and eventually this can cause the cells to burst

Question 8

What is the word equation for respiration?

Answer 8

Glucose + oxygen —–> carbon dioxide + water

Question 9

What is the purpose of respiration?

Answer 9

To release energy

Question 10

What is the chemical equation for respiration?

Answer 10

C6H12O6 + 6O2 —-> 6CO2 + 6H2O

Question 11

When does respiration take place?

Answer 11

During the day and night

Question 12

How does photosynthesis work?

Answer 12

• Light energy is absorbed by the chlorophyll, which is the green pigment found inside the chloroplasts
• This energy is used to turn carbon dioxide and water into glucose and oxygen

Question 13

How is the epidermis adapted?

Answer 13

It is a thin, transparent layer to allow sunlight to get through to the palisade cells

Question 14

How is the palisade mesophyll adapted?

Answer 14

• It is the main site of photosynthesis, so has lots of chloroplasts
• which are positioned at the top of the leaf and are close to each other to absorb as much sunlight as possible

Question 15

How is the spongy mesophyll adapted?

Answer 15

• The chloroplasts are not closely packed together and have irregular shapes, which creates air spaces
• So this allows gases to diffuse quicker, so gas exchange is more efficient

Question 16

What is the stomata?

Answer 16

It is a hole or pore on the underside of the leaf , it is where gas exchange takes place

Question 17

What do guard cells do?

Answer 17

They control the size of the stomata

Question 18

Why do the guard cells go turgid when the plant has lots of water?

Answer 18

It makes the stomata open so gases can be exchanged for photosynthesis

Question 19

What are 6 ways the guard cells are adapted to open and close the stomata?

Answer 19

1. They have a kidney shape which opens and closes the stomata
2. When the plant has lots of water the guard cells fill with it and go plump and turgid
3. When the plant is short of water, the guard cells lose water and become flaccid
4. Thin outer walls and thickened inner walls to make the opening and closing work
5. They are sensitive to light and close at night to save water without losing out on photosynthesis
6. More stomata is usually found on the underside of the leaf rather than the top. This lower surface is shaded and cooler, so less water is lost through the stomata than if they were on the upper surface

Question 20

Why is the stomata open during the day?

Answer 20

• During the day, water moves into the cell via osmosis, this causes the guard cells to be turgid
• So this opens up the stomata because during the day photosynthesis is taking place, so carbon dioxide is needed
• So if the stomata is open carbon dioxide is able to enter the leaf via diffusion

Question 21

Why is the stomata closed during the night?

Answer 21

• At night, water leaves the guard cells so they become flaccid, so the stomata closes
• This means less water is lost via evaporation/diffusion, so the plant does not become dehydrated

Question 22

What is the structure of the xylem?

Answer 22

• the xylem is made up of dead cells
• it is composed of hollow tubes strengthened by lignin

Question 23

What is lignin?

Answer 23

a carbohydrate material lining the xylem vessels providing strength and support

Question 24

What is the structure of the phloem?

Answer 24

• the phloem consists of living cells
• phloem has pores in the end walls for cell sap to move through one phloem cell to the next
• consist of sieve tubes which have no nuclei
• companion cells in the phloem provide energy for translocation

Question 25

Does transport in the xylem require energy?

Answer 25

no, as it is a passive process

Question 26

Does transport in the phloem require energy?

Answer 26

yes, as it is an active process

Question 27

In what direction are substances transported in the xylem?

Answer 27

up, in one direction

Question 28

In what direction are substances transported in the phloem?

Answer 28

up and down, in both directions