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Flashcards in B4 Deck (38):
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Define: photosynthesis

• The process in which green plants make their own food (glucose and starch) using sunlight

1

Photosynthesis produces glucose for biomass and energy. Oxygen is released as a by product. What is the word and symbol equation for photosynthesis?

Light
Carbon dioxide + water -------> glucose + oxygen
Chlorophyll
6CO2 + 6H2O ---> C6H12O6 + 6O2

2

How was the theory of photosynthesis gradually accepted?

• Greeks - plants gained mass by taking in minerals though soil
• Van Helmont - plant growth cannot be solely due to nutrients in soil
• Joseph Priestly - put a plant in a jar if air, and a plant in a jar with a mouse inside. He changed combinations of plants and mouse and concluded that oxygen is produced by plants

3

Glucose can either be...

• Used straight away to produce energy through respiration
• Converted in substances that the plant needs

4

What are the properties of glucose?

• Soluble
• Transported around the plant as soluble sugar
• But must be converted into starch, which is insoluble, in order to be stored

5

Glucose and starch can be converted into:

• Energy (respiration)
• Proteins for growth + repair
• Starch, days or oils that can be stored in seeds
• Cellulose which is needed for plant cell wall

6

Why is starch such a useful storage molecule?

• Insoluble so it doesn't affect the water concentration inside cells
• It does not move away in solution from storage areas
- If the cells stored soluble glucose, the inside if the cells would become very concentrated and water would constantly move in through osmosis, which would make the cell swell

7

Photosynthesis can be increased by increasing:

• the temperature - using heaters in a greenhouse
• the light intensity - using lamps in greenhouse
• the carbon dioxide - CO2 concentration is increased by chemicals

8

Describe the effect of temperature of photosynthesis.

• As temperature rises, so does the rate pd photosynthesis
• This means temperature is the limiting factor in rate of photosynthesis
• As the temperature reaches 45°C, the enzymes controlling photosynthesis start to become denatured
• Once denatured the rate declines to zero

9

Describe the effect of carbon dioxide concentration on the rate of photosynthesis.

• As the concentration rises, so does the rate of photosynthesis
• Carbon dioxide is limiting the rate of photosynthesis, up until a certain point
• After this point, a rise in carbon dioxide levels makes no difference
• So, carbon dioxide is no longer a limiting factor; light or temperature must be

10

Describe the effect of flight intensity on the rate of photosynthesis.

• As light intensity rises so does the rate of photosynthesis
• This means light is a limiting factor up to a certain point
• After a certain point, a rise in the light intensity has no effect
• Light intensity is no longer the limiting factor; carbon dioxide or temperature must be

11

Explain respiration through night and day.

• During the day light is readily available from the sun so plants photosynthesise; taking in carbon dioxide to make glucose and releasing oxygen as a by-product

12

What is the chlorophyll in a leaf?

• Contains a pigment called chlorophyll (which absorbs light) in millions of chloroplasts
• Plus other pigments to absorb light from different parts of the spectrum

13

Describe the surface area of a leaf?

• Broad and flat
• Provides huge surface area to absorb sunlight

14

What do vascular bundles in a leaf do?

• Needed for support and to transport water to the cells
• Removes the products of photosynthesis such as glucose

15

Why does a leaf have such a thin structure?

• So that gases (carbon dioxide and oxygen) only have a short distance to travel to and from the cells

16

What does the stomata do?

• Stomata are essentially tiny pores
• On the underside of the leaf to allow the exchange of gases
• They are opened and closed by guard cells

17

What happens in a plant during photosynthesis?

• Carbon dioxide diffuses in through the stomata (leaf pores)
• Oxygen diffuses out the stomata
• Water is absorbed by the roots

18

What are the four distinct layers in a leaf?
What are the properties of each layer?

• Upper epidermis - transparent to allow sunlight to the later below
• Palisade layer - where the cells are near to the top of the leaf and are packed with chloroplasts so they can absorb the maximum amount of light
• Spongy mesophyll - contains lots of air spaces connected to the stomata to allow the optimum exchange of gases
• Lower epidermis
* This internal structure provides a high surface area to volume ratio for efficient gas exchange*

19

What is specialised about the shape of a chloroplast in appellant cell and why aren't they in all plant cells?

• They are long to absorb lots of light
• Not found in all cells
• Such as root cells as they don't receive any light

20

Define: diffusion

• Substances move in and out of cell membranes by diffusion.
• It's the movement of a substance from a region of high concentration to a region of low concentration

21

Describe the particle movement in diffusion?

• Particles move about in lots of different directions
• Random movement
• Net (overall) movement of of particles from an area of high concentration to an area of low concentration

22

What increases the rate of diffusion?

• There's a greater surface area of the cell membrane
• There's a steeper concentration gradient
• The particles have a shorter distance to travel

23

What do oxygen and carbon dioxide do during the day?

• Carbon dioxide is used up in photosynthesis (The concentration inside the leaves is lower than outside them
• Carbon dioxide diffuses into the plant through the stomata on the underside of the leaf
• Oxygen diffuses from the plant into the atmosphere

24

What happen to carbon dioxide and oxygen in the night?

• Photosynthesis stops
• Oxygen diffuses into leaf cells
• Carbon dioxide diffuses out of leaf cells
• The stomata on the underside of the leaves are specially adapted to:
- open to help increase the rate of diffusion of carbon dioxide and oxygen
- close to prevent excessive water loss in drought conditions

25

What are the purposes of the four main mineral essential for healthy plant growth?

• Nitrates - to make amino acids that form proteins
• Potassium - is used to help enzymes in respiration and photosynthesis
• Phosphates - are used to make DNA and cell membranes
• Magnesium - is used to make chlorophyll for photosynthesis

26

What are the visible results of lack of the four main minerals in plants?

• Lack of nitrates - poor growth, yellow leaves
• Lack of potassium - poor flower + fruit growth, discoloured leaves
• Lack of phosphates - poor root growth, discoloured leaves
• Lack of magnesium - yellow leaves

27

Define: biological control

• Where a farmer introduces a predator, instead of using pesticide, to reduce the number of pests

28

Advantages of biological control

• The predator selected only usually attacks the pest (specie specific)
• Once introduced, the predator can have an impact over many years, so repeating treatment isn't required
• The pest can't become resistant to the predator (unlike pesticides)
• No need for chemical pesticides

29

Disadvantages of biological control

• The pest reduces but isn't completely removed
• The predator may not eat the pest or it may even eat useful species
• The predator may reproduce uncontrollably
• The predator may leave the area

30

Advantages of hydroponics

• The mineral levels added to the solution can be carefully controlled and adjusted to the type of plant
• The risk if the plants becoming diseased is reduced

31

Disadvantages of hydroponics

• Plants must be supported as they have no anchorage for their roots
• Expensive fertilisers are needed to supply the plant with minerals

32

Define: organic farming

• Organic farming methods aims to produce food without the use of chemicals, so minimising the impact on the environment (no pesticides or artificial fertilisers)

33

List some organic farming methods.

• Using natural fertilisers such as animal manure or compost
• Growing nitrogen-fixing crops such as peas or clover
• Rotating crops to maintain soil fertility
• Avoiding chemical pesticides by weeding
• Varying seed planting times to discourage pests

34

Advantages of organic farming.

• Food crops and environment aren't damaged by artificial fertilisers and pesticides
• Soil erosion is limited, and fertility is maintained through the use of organic fertilisers
• Biodiversity is promoted because hedgerow and other habitats are conserves
• Livestock have space to roam

35

Disadvantages of organic farming

• It's less efficient because some crops are lost to pests and diseases
• Organic fertilisers take time to rot and they don't supply a specific balance of materials
• It is expensive
• More space is needed

36

What are vascular bundles?

• The xylem and phloem form a continuous system of tubes from roots to leaves

37

What does the xylem do? How are they adapted to do this?

• Transports water and soluble mineral salts from the roots to the leaves (transpiration)
• Xylem vessels are made from dead plant cells. They have a hollow lumen.
• The cellulose cell walls are thickened with a waterproof substances