B4 - Photosynthesis

Question 1

Give the word and symbol equation for photosynthesis

Answer 1

sunlight
Carbon dioxide + water -> carbohydrates + oxygen
6CO2 + 6H20 -> C6H12O6 + 6O2
chlorophyll

Question 2

What are the two stages of photosynthesis ?

Answer 2

• The first = light energy to split water into waste oxygen gas and hydrogen ions.
• The second = ( occur day or night) - combines hydrogen ions with carbon dioxide to form glucose and some water.

Question 3

What does the plant make in photosynthesis and what is it used for?

Answer 3

1. Food: this is glucose, a carbohydrate. Some is used for
   respiration in the plant’s cells. The rest can be stored in
   the plant.
2. Oxygen: this is a waste gas produced in photosynthesis.
   Some is used for respiration in the plant’s cells. The rest is given off through the stomata into the plant’s surroundings.

Question 4

What can glucose be converted to and why?

Answer 4

• may be used to make sucrose. good for transport because it dissolves in water and flows easily.
• can be changed into starch and stored until it is needed. Can be used for respiration at night, when there is no sunlight and the plant is not making glucose by photosynthesis.
• can convert sugar to cellulose, proteins, and fats, which it needs to grow and for other functions.

Question 5

What are the advantages of storing glucose as starch?

Answer 5

1. Starch can be converted back into glucose for
   respiration in plant cells.
2. Starch is insoluble and so will not dissolve in water
   and flow out of the cells where it is stored.
3. Starch does not affect the water concentration inside
   the cells.

Question 6

What is the difference between plants during day and night?

Answer 6

Day time : - rate of photosynthesis > rate of respiration
- take in more carbon dioxide for photosynthesis and release the extra oxygen produced.

Night time : - respire but do not photosynthesise.
- Oxygen is taken into the leaf and waste carbon dioxide is released.

Question 7

What factors will speed up photosynthesis and why?

Answer 7

• more carbon dioxide -> Carbon dioxide is one of the raw materials for photosynthesis. The more carbon dioxide there is available, the faster the rate of photosynthesis.
• more light -> Light provides the energy to drive photosynthesis. The more light there is, the faster the rate of photosynthesis.
• warmer temperature -> Temperature affects how quickly enzymes work. Enzymes make the reactions of photosynthesis happen. As the temperature rises, the rate of photosynthesis increases (providing there is plenty of carbon dioxide and light). However, if it becomes too hot the enzymes will be denatured and photosynthesis stops.

Question 8

Define the term limiting factor

Answer 8

limiting factor - the one that is at the lowest level will be the factor which limits the rate of reaction.

Question 9

Describe the structure of a leaf

Answer 9

-------------- > cuticle 
OooooooooooO > upper epidermis 
Ôoôoôoôoôoôoô
Oôoôoôoôoôoôo > palisade mesophyll layer 
         O ooooo 
Ooo o.           Oooo
O.                         O > spongy mesophyll layer 
Ooo.            Oooooo
        Ooooooo
Oooooooooooooo> Lower epidermis 
-------------------> lower cuticle

Question 10

Explain the structure of a leaf

Answer 10

• The outer epidermal cells are transparent to allow light through.
• The palisade and spongy mesophyll cells are full of chloroplasts. Chloroplasts contain the chlorophyll and other pigments that absorb light energy for photosynthesis.
• In the lower epidermis, pores called stomata are protected by guard cells that open and close to allow gases in and out.

Question 11

Describe some adaptations of the leaf for photosynthesis

Answer 11

✓ The upper palisade layer, which receives the most light, contains the most chloroplasts.
✓ There are air spaces in the spongy mesophyll layer to allow carbon dioxide to diffuse from the stomata to the palisade cells.
✓ The air spaces inside the leaf give a large surface area to volume ratio. This allows maximum absorption of gases.
✓ The epidermis is transparent.

✓ Many leaves are broad and at, giving a large surface ✓ area to absorb as much light as possible.
✓ Leaves are thin, providing a short diffusion pathway for carbon dioxide to diffuse to the mesophyll and palisade cells.
✓ Theleafcellscontainchlorophyllandotherpigments that absorb energy from different parts of the spectrum.
✓ The cells of the palisade layer are neatly packed in rows, to t more cells in.
✓ Veins contain vascular bundles. These form a network that supports the leaf blade. They also carry water from the root to the leaf, and carry soluble sugars away.
There are plenty of stomata, pores in the lower epidermis, which allow carbon dioxide in and oxygen out. Guard cells control whether they are open or closed.