Photosynthesis

Question 1

What is the purpose of photosynthesis?

Answer 1

For plants to convert sunlight, water and carbon dioxide into glucose

Question 2

What is the equation for photosynthesis?

Answer 2

water + carbon dioxide + (sunlight)–> glucose + oxygen

Question 3

Where does photosynthesis occur in the cell?

Answer 3

In the chloroplast

Question 4

Describe two features of the grana/thylakoid discs that increase the rate of photosynthesis

Answer 4

The thylakoid discs are flattened which increases the surface area to absorb more sunlight to increase photosynthesis rate
The grana/thylakoid discs contain chlorophyll which absorbs energy from the sun for photosynthesis

Question 5

Describe a feature of the stroma that increases the rate of photosynthesis

Answer 5

The stroma is a liquid interior in which the conditions are optimum for enzymes (pH, temperature) to increase photosynthesis rate

Question 6

Describe a feature of the shape of the chloroplast that increases the rate of photosynthesis

Answer 6

The chloroplast is bean shaped to increase the surface area so water can be absorbed faster by omosis and carbon dioxide absorbed faster by diffusion.

Question 7

Describe what happens, location and products of the light dependent reaction in photosynthesis

Answer 7

Occurs in the thylakoid discs/grana
Light energy is used to split up water (hydrolysis)
Oxygen is produced which moves out of the chloroplast by diffusion.
Hydrogen also produced which moves on to the light independent reaction
ATP is produced which is used in the light independent reaction

Question 8

Describe what happens, location and products of the light independent reaction in photosynthesis

Answer 8

Occurs in the stroma

Carbon dioxide and hydrogen are combined to form glucose using ATP

Question 9

Where in a cell would you find chloroplasts?

Answer 9

Near the outer edges of the cells just inside the cell membrane

Question 10

Explain two reasons why chloroplasts are found near the outre edges of cells

Answer 10

They receive a higher light intensity there which will increase the rate of photosynthesis
Faster to transport the substrates for photosynthesis (carbon dioxide by diffusion, water by osmosis) from outside the cell to the inside edges rather than the middle which increases the rate of photosynthesis

Question 11

Why do palisade cells have large vacuoles in the middle of the cell?

Answer 11

Vacuoles are used purely for storage. The cell is less efficient at transporting the reactants for photosynthesis to the centre of the cell.

Question 12

What is the waxy transparent layer on top of a leaf called?

Answer 12

Cuticle

Question 13

Why do leaves have cuticles linked to photosynthesis?

Answer 13

So they conserve water which is a substrate needed for photosynthesis

Question 14

Why is the upper epidermis of a leaf transparent?

Answer 14

To let a higher light intensity reach the palisade cells which is is the main site of photosynthesis, hence a faster rate

Question 15

What cells in the leaf contain the most chloroplasts?

Answer 15

Palisade cells

Question 16

Where are these palisade cells located in the leaf and why?

Answer 16

They are near the top of the leaf so they receive a high light intensity for a faster rate of photosynthesis

Question 17

Why does the spongy mesophyll cell layer have air spaces?

Answer 17

To allow carbon dioxide entering the leaf through the stomata to diffuse easily through to the palisade cells as it is a substrate of photosynthesis.
Allows oxygen, a product of photosynthesis, to diffuse easily from the palisade cells out to the stomata

Question 18

What is the functions of the stomata?

Answer 18

To allow carbon dioxide to diffuse into and water to diffuse out of the inside of the leaf

Question 19

Why are stomata found on the lower side of the leaf?

Answer 19

Water can be lost out of the stomata. The lower side is cooler than the upper side so less water would be lost out of the stomata

Question 20

Why does increasing light intensity initially increase the rate of photosynthesis?

Answer 20

Increasing light intensity means there is more energy being absorbed by chlorophyll in the chloroplasts. Therefore more water molecules can be broken up in the light dependent phase and hence a faster rate of photosynthesis.

Question 21

Why does the rate of photosynthesis level off and become constant as light intensity continues to increase?

Answer 21

Photosynthesis is occurring at its maximum rate because other factors are limiting and stop it increasing further e.g. carbon dioxide, water, number of chloroplasts/amount of chlorophyll

Question 22

How does water get brought to the leaf?

Answer 22

From the roots through the xylem cells in the vascular bundle. It moves by osmosis

Question 23

Why does increasing the substrate concentration i.e. water or carbon dioxide, initially increase the rate of photosynthesis?

Answer 23

There are more substrate particles per ml therefore are more collisions per second between the substrate particles and the enzymes’ active sites who control photosynthesis. Therefore the rate at which glucose is made increases

Question 24

Why does the rate of photosynthesis not keep increasing but instead levels off at a constant rate despite an continuing increase in substrate concentration.

Answer 24

If there is a fixed number of enzymes, there is a limited number of active sites and so all of the enzymes active sites are full and photosynthesis is operating at its maximum rate

Question 25

With increasing sunlight and a changing of the seasons, temperature can increase. Why does this increase the rate of photosynthesis?

Answer 25

As the temperature increases, the substrates particles e.g. carbon dioxide/water have more energy, they move faster increasing the number of collisions per second with the enzymes active sites.

Question 26

At high temperatures, the rate of photosynthesis slows down and will eventually stop - why?

Answer 26

At high temperatures, the enzymes denature. The hydrogen bonds that hold their active sites in shape break and they change shape which means than the substrate particles i.e. carbon dioxide/water can no longer fit in to them and glucose cannot be produced.

Question 27

Minerals such as copper act as enzyme inhibitors which slows down the rate of photosynthesis - how?

Answer 27

The enzymes inhibitors either fill up the active sites (competitive inhibitors) or change the shape of the enzyme’s active sites (non-competitive inhibitors) which means that the substrate particles (water/carbon dioxide) can no longer fit in and be converted into glucose

Question 28

Other substances can act as enzyme cofactors or co enzymes. Explain how these increase the rate of enzyme activity

Answer 28

Enzyme cofactors either help complete the shape of the active site with the substrate of help alter the active site to better fit the substrate which speeds up the conversion to glucose

Question 29

How might the pH affect the rate of photosynthesis?

Answer 29

If the pH is optimum for that plant, photosynthesis will occur at its fastest rate. More alkaline (basic) or acidic than this will break the hydrogen bonds in the enzyme which changes the shape of its active site. Substrate particles (water/carbon dioxide) can no longer fit in and be converted into glucose.