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Flashcards in Plants and Food Deck (54)
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1
Q

How can you prevent a plant from making starch?

A

Deprive it from light OR put it in a closed container containing soda like which absorbs all the carbon dioxide in the air.

2
Q

What is the main storage carbohydrate made by plants?

A

Starch

3
Q

How can you show that plants produce oxygen in light?

A

Use an aquatic plant and place a piece of this plant, for example elodea, in a test tube under bright light. It will produce a stream of bubbles. Collect these and test their contents for oxygen. They should contain a high concentration of oxygen.

4
Q

How do plants make starch?

A

Starch is composed of long chains of glucose. A plant first makes glucose, which is then joined together in chains to make starch molecules.

5
Q

Word equation for photosynthesis:

A

Carbon dioxide + water —> glucose + oxygen (Light and chlorophyll on the arrow)

6
Q

What is the role of the chlorophyll?

A

It is a green pigment that absorbs all the light energy needed to take place.

7
Q

What does photosynthesis do?

A

Converts light energy into chemical energy.

8
Q

Chemical equation for photosynthesis:

A

6H20 + 6C02 —> C6H12O6 + 6O2

9
Q

Why is photosynthesis important? (2)

A

Because it allows plants to make glucose (food)

Because it produces oxygen for all animals and plants that respire aerobically

10
Q

What type of nutrition is photosynthesis?

A

Autotrophic

11
Q

What does respiration do?

A

Releases energy from the breakdown of glucose. This chemical energy came originally from the light ‘trapped’ by the process of photosynthesis.

12
Q

What do leaves need to be able to photosynthesise efficiently?

A

1) Large surface area to absorb light. 2) many chloroplasts containing chlorophyll 3) a supply of water and carbon dioxide 4) a system for carrying away the products of photosynthesis to other parts of the plant

13
Q

What are the outer layers of cells of a leaf and what are their functions?

A

The outer layers of cells are the upper and lower epidermis which have few chloroplasts and are covered by a thin layer of wavy material called the cuticle. This reduces water loss by evaporation and acts as a barrier to the entry of disease causing microorganisms so such as bacteria and fungi.

They are also transparent which allows light to pass through the epidermis to the chloroplasts in the palisade layer

14
Q

Where are the stomata found and what are their function?

A

In the lower epidermis there are many pores called stomata (one stoma). These allow carbon dioxide to diffuse into the leaf, to reach photosynthetic tissues. They also allow oxygen and water vapour to diffuse out.

15
Q

What is a stoma?

A

Each stoma is formed as a gap between two highly specialised cells called guard cells. The guard cells can alter their shape to open or close the stoma.

16
Q

Where is the palisade layer found and what is its function?

A

Just below the upper epidermis is a palisade layer made from elongated cells, each containing hundreds of densly packed chloroplasts which absorb light and is the main site of photosynthesis. They are close to the source of light and the upper epidermis is relatively transparent allowing light to pass though.

17
Q

What is below the palisade cells? What is its function?

A

The spongy mesophyll layer. These cells also photosynthesise but have less chloroplasts that the palisade cells. They form the main gas exchange surface of the leaf, absorbing carbon dioxide and releasing oxygen and water vapour.

18
Q

Why do the spongy mesophyll have air spaces?

A

To allow oxygen, carbon dioxide and water vapour to diffuse in and out of the mesophyll.

19
Q

What is a gas exchange surface?

A

A tissue that allows gases (usually oxygen, carbon dioxide and water vapour) to pass across it between the plant or animal and the outer environment. They have a large surface area to volume ratio which allows large amounts of gases to diffuse across.

20
Q

How are water and mineral ions supplied to the leaf?

A

By vessels in a tissue called the xylem. This forms a continuous transport system throughout the plant. Water is absorbed by the roots and passes up though the stem and though veins in the leaves in the transpiration stream. In the leaves, water leaves the xylem and supples the mesophyll cells.

21
Q

How are the products of photosynthesis carried in the leaf?

A

They are carried away from the mesophyll cells by the phloem. This supplies all other parts of the plant so that the tissues and organs that can’t make their own food receive the products of photosynthesis.

22
Q

When will a plant produce more carbo dioxide than it uses?

A

In dim light as it cannot carry out carbon dioxide efficiently but it continues to produce carbon dioxide as a product of respiration.

23
Q

How does the concentration of carbon dioxide in the air change throughout the day?

A

It is an upside down bell curve with the lowest point being noon.

24
Q

Why is the concentration of carbon dioxide around a plant different at different times of day?

A

At noon the sun will be directly above the plant and photosynthesis will be happening at its highest rate meaning carbon dioxide is used up faster. At night when there is no photosynthesis as there is no light, the level of carbon dioxide rises. This is because whilst no carbon dioxide is being absorbed by plants. It is still added to the air by respiration of all the organisms in the area.

25
Q

What do plants you glucose for?

A

In a plant glucose is converted into:

  • starch for storage
  • other sugars like fructose or sucrose which is the main sugar carried in the phloem
  • the polymer cellulose, which forms plant cell walls
  • lipids for the membrane of all cells and an energy store in seeds and fruits
  • proteins and DNA (when mineral ions from soil is added)
  • chlorophyll (when magnesium ion for soil is added)
26
Q

How can glucose be used for so many things?

A

Carbohydrates and lipids both contain only 3 elements - carbon, hydrogen and oxygen. This means they can be inter-converted without the need for a supply of other elements.

Proteins contain these elements too, but all amino acids contain nitrogen as well which is why nitrate ions are obtained through a plants roots.

27
Q

Why do plants need mineral ions and how do they get them?

A

For healthy growth and they are absorbed through the roots as the mineral ions are dissolved in the soil water

28
Q

What two important mineral ions do plants need?

A

Magnesium and Nitrate

29
Q

Why do plants need nitrate ions?

A

To make amino acids, which are needed to make proteins and needed for the growth of new cells.

Also needed to make chlorophyll, DNA and many other compounds.

30
Q

Why do plants need magnesium ions?

A

To make chlorophyll

31
Q

Why do plants need potassium ions?

A

For enzymes of respiration and photosynthesis to work

32
Q

Why do plants need phosphate ions?

A

making DNA and many other compounds, part of cell membranes

33
Q

How does varying light intensity affect the rate of photosynthesis?

A

With insufficient light, a plant can not photosynthesise very quickly, even if there is water and co2 Increasing the light intensity will increase the rate of photosynthesis

34
Q

How does varying carbon dioxide concentration affect the rate of photosynthesis?

A

The rate of photosynthesis increases if there is a higher carbon dioxide concentration and if there is insufficient carbon dioxide a plant cannot photosynthesise

35
Q

How does temperature affect the rate of photosynthesis?

A

If the temperature is too cold, the rate of photosynthesis will decrease Plants cannot photosynthesise if it is too hot. There is an ideal temperature when photosynthesis is best (the graph is a sad face)

36
Q

What is the main Storage carbohydrate made by plants?

A

Starch

37
Q

How do you test for starch?

A

Add a few drops of the iodine solution, it the colour turns blue/black there is starch present. If not it is orangey yellow.

38
Q

Why can you not test for starch on a new fresh leaf?

A

The outer waxy surface layer will not absorb the solution and the green colour will hide the colour change.

39
Q

What must you do before you place the iodine solution on the leaf when testing for starch?

A

The leaf must be decolorised and the outer waxy layer must be removed. This is done by placing the leaf in boiling ethanol.

40
Q

Give an example of an experiment to show that starch is only produced in the parts of plants that are green.

A

Test the starch on a VARIAGATED leaf and you will see that the white regions that don’t contain chlorophyll are my positive for starch.

41
Q

What must you take caution with when heating ethanol?

A

Do not heat the tube directly but in a beaker filled with water as ethanol is highly flammable.

42
Q

Write a method for the rest of starch in a leaf.

A

A beaker of water is set up on a tripod and the water is heated until it boils. A leaf is removed from a plant and killed by placing it in the water for 30 seconds. (This stops all chemical reactions in the leaf). The Bunsen burner is turned off, the leaf placed in a boiling tube containing ethanol, and the tube stood in the beaker of hot water. B.P. of ethanol is lower than that of water to it will boil for a few minutes until the water cools down. Long enough to remove most of the chlorophyll from the leaf. When the leaf has turned colourless it is removed and washed in cold water then spread out on a tile and covered with a few drops of iodine and after a few minutes any parts of the leaf that contained starch will turn blue or black.

43
Q

How can you show that plants produce oxygen when in light?

A

Place an aquatic plant (elodea) in a test tube of water under a bright light. It produces a stream of small bubbles. If the bubbles are collected and their contents analysed, they are found to contain a high concentration of oxygen.

44
Q

Give an experiment to show that carbon dioxide is needed in photosynthesis?

A

A plant is surrounded with a glass bell jar and inside it is soda lime. There is light on the plant but the soda lime absorbs the carbon dioxide from the air in the bell jar. A control experiment should be set up wih the exact same apparatus but without the soda lime or with sodium hydrocarbonate to provide CO2. Comment on the effect of the plant without CO2.

45
Q

What is the role of chlorophyll?

A

To absorb the light energy needed for photosynthesis to take place.

46
Q

What would you use to indicate change in CO2 levels?

A

Hydrocarbonate indicator solution.

47
Q

What are the colour changes with Hydrocarbonate indicator solution?

A

High conc. = yellow Normal air conc. = orange Low conc. = purple

48
Q

Give an experiment to investigate the effect of light on photosynthesis.

A

10cm3 of hydrocarbonate indicator solution is placed in the bottom of four boiling tubes. Three large leaves are placed at the top of each tube and they are sealed with a bung. One is the control so there is no leaf. One tube is in light, one in the dark covered with silver foil, one dim light and in the control light.

49
Q

What would the colour of the Hydrocarbonate indicator solution be at the end of this experiment for the four tubes?

A

The leaf in light would be purple (low CO2) Leaf in dark would be yellow (high CO2) Leaf in dim would be orange as well as control (normal CO2).

50
Q

Explain the conc. of CO2 in this experiment (the four test tube leaf one)

A

The leaf in the light would be respiring and photosynthesising but photosynthesis would be happening at a faster rate so more CO2 would be used up and there would be a lower conc. in the test tube. The leaf in the dark would be respiring at a faster rate than photosynthesising because there is no light so photosynthesis would not happen. This means there would be a high conc of CO2 as it is produces but not used up. Dim light means respiration and Photosynthesis are happening at a similar rate so the CO2 level is normal.

51
Q

Why does increased oxygen in soil help plants to grow

A

Oxygen is used in respiration. The energy released in respiration helps the roots carry out active transport so that mineral ions can enter the plant

52
Q

Explain how less plants can help the plants that are there grow

A

Less plants reduced competition for eg mineral ions and light

53
Q

Why do plants absorb any other colour light better than green light?

A

Because chlorophyll in plants is green so it reflects the green light more.

54
Q

How are the stomata adapted for gas exchange?

A