2. Chapter: Plant Processes
Table of Contents
Chapter: Plant Processes
Section 1: Photosynthesis and
Respiration
Section 2: Plant Responses

3. Taking in Raw Materials
Photosynthesis and Respiration 1
Taking in Raw Materials
Food is one of the raw materials you need to grow. Oxygen is another.
Your cells use oxygen to help release energy from the food that you eat.
“Does a tree need to eat? Does it use oxygen? How does it get rid of wastes?”

4. Movement of Materials in Plants
Photosynthesis and Respiration 1
Movement of Materials in Plants
Plants make their own foods using the raw materials water, carbon dioxide, and inorganic chemicals in the soil.
Plants also produce waste products.
Most of the water used by plants is taken in through roots. Water moves into root cells and then up through the plant to where it is used.

5. Movement of Materials in Plants
Photosynthesis and Respiration 1
Movement of Materials in Plants
Leaves, instead of lungs, are where most gas exchange occurs in plants.
Carbon dioxide, oxygen, and water vapor exit and enter the plant through openings in the leaf.

6. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
A leaf is made up of many different layers.
The outer cell layer of the leaf is the epidermis. A waxy cuticle that helps keep the leaf from drying out covers the epidermis.

7. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
If you examine the epidermis under a microscope, you will see that it contains many small openings.
These openings, called stomata (stoh Mah tuh) (singular, stoma), act as doorways for raw materials such as carbon dioxide, water vapor, and waste gases to enter and exit the leaf.

8. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
Stomata also are found on the stems of many plants.
More than 90 percent of the water plants take in through their roots is lost through the stomata.

9. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
Two cells called guard cells surround each stoma and control its size.
As water moves into the guard cells, they swell and bend apart, opening a stoma.
When guard cells lose water, they deflate and close the stoma.

10. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
Stomata usually are open during the day, when most plants need to take in raw materials to make food.
They usually are closed at night when food making slows down. Stomata also close when a plant is losing too much water.

11. Leaf Structure and Function
Photosynthesis and Respiration 1
Leaf Structure and Function
Inside the leaf are two layers of cells, the spongy layer and the palisade layer.
Carbon dioxide and water vapor fill the spaces of the spongy layer.
Most of the plant’s food is made in the palisade layer.

12. Chloroplasts and Plant Pigments
Photosynthesis and Respiration 1
Chloroplasts and Plant Pigments
Most leaves look green because some of their cells contain so many chloroplasts.
Chloroplasts are green because they contain a green pigment called chlorophyll (KLOR uh fihl).

13. Chloroplasts and Plant Pigments
Photosynthesis and Respiration 1
Chloroplasts and Plant Pigments
A pigment is a substance that reflects a particular part of the visible spectrum and absorbs the rest.
When you see a green leaf, you are seeing green light energy reflected from chlorophyll.

14. Chloroplasts and Plant Pigments
Photosynthesis and Respiration 1
Chloroplasts and Plant Pigments
In fall, the chlorophyll in some leaves breaks down and the leaves change color as other pigments become visible.

15. Chloroplasts and Plant Pigments
Photosynthesis and Respiration 1
Chloroplasts and Plant Pigments
Pigments, especially chlorophyll, are important to plants because the light energy that they absorb is used to make food.

16. Chloroplasts and Plant Pigments
Photosynthesis and Respiration 1
Chloroplasts and Plant Pigments
For plants, this food-making processphotosynthesishappens in the chloroplasts.

17. The Food-Making Process
Photosynthesis and Respiration 1
The Food-Making Process
Photosynthesis (foh toh SIHN thuh suhs) is the process during which a plant’s chlorophyll traps light energy and sugars are produced.
Pigments, especially chlorophyll, are important to plants because the light energy that they absorb is used to make food.

18. The Food-Making Process
Photosynthesis and Respiration 1
The Food-Making Process
For example, photosynthesis occurs only in a carrot plant’s lacy green leaves.
Excess sugar produced in the leaves is stored in the familiar orange root that you and many animals eat.

19. The Food-Making Process
Photosynthesis and Respiration 1
The Food-Making Process
Besides light, plants also need the raw materials carbon dioxide and water for photosynthesis.
The overall chemical equation for photosynthesis is shown.

20. Light-Dependent Reactions
Photosynthesis and Respiration 1
Light-Dependent Reactions
During light-dependent reactions, chlorophyll and other pigments trap light energy that eventually will be stored in sugar molecules.
Light energy causes water molecules, which were taken up by the roots, to split into oxygen and hydrogen.

21. Light-Dependent Reactions
Photosynthesis and Respiration 1
Light-Dependent Reactions
The oxygen leaves the plant through the stomata.
Hydrogen produced when water is split is used in photosynthesis reactions that occur when there is no light.

22. Light-Independent Reactions
Photosynthesis and Respiration 1
Light-Independent Reactions
Reactions that don’t need light are called the light-independent reactions of photosynthesis.
The light energy trapped during the light-dependent reactions is used to combine carbon dioxide and hydrogen to make sugars.
One important sugar that is made is glucose. The chemical bonds that hold glucose and other sugars together are stored energy.

23. Light-Independent Reactions
Photosynthesis and Respiration 1
Light-Independent Reactions

24. Light-Independent Reactions
Photosynthesis and Respiration 1
Light-Independent Reactions
What happens to the oxygen and glucose that were made during photosynthesis?
Most of the oxygen from photosynthesis is a waste product and is released through stomata.
Glucose is the main form of food for plant cells.
A plant usually produces more glucose than it can use. Excess glucose is stored in plants as other sugars and starches.

25. Light-Independent Reactions
Photosynthesis and Respiration 1
Light-Independent Reactions
Glucose also is the basis of a plant’s structure.
Cellulose, an important part of plant cell walls, is made from glucose.
Leaves, stems, and roots are made of cellulose and other substances produced using glucose.
The products of photosynthesis are used for plant growth.

26. Importance of Photosynthesis
Photosynthesis and Respiration 1
Importance of Photosynthesis
Organisms that carry on photosynthesis provide food directly or indirectly for nearly all the other organisms on Earth.

27. Importance of Photosynthesis
Photosynthesis and Respiration 1
Importance of Photosynthesis
Photosynthetic organisms use carbon dioxide and release oxygen. This removes carbon dioxide from the atmosphere and adds oxygen to it.

28. Photosynthesis and Respiration1
The Breakdown of Food
Respiration is a series of chemical reactions that breaks down food molecules and releases energy. Respiration occurs in cells of most organisms.

29. Photosynthesis and Respiration1
The Breakdown of Food
Respiration that uses oxygen to break down food chemically is called aerobic respiration.
In plants and many organisms that have one or more cells, a nucleus, and other organelles, aerobic respiration occurs in the mitochondria (singular, mitochondrion). The overall chemical equation for aerobic respiration is shown.

30. Photosynthesis and Respiration1
Aerobic Respiration
Aerobic respiration takes place in the mitochondria of plant cells.

31. Photosynthesis and Respiration1
Aerobic Respiration

32. Importance of Respiration
Photosynthesis and Respiration 1
Importance of Respiration
Respiration changes food energy into a form all cells can use. This energy drives the life processes of almost all organisms on Earth.
The waste product carbon dioxide is also important.
Aerobic respiration returns carbon dioxide to the atmosphere, where it can be used again by plants and some other organisms for photosynthesis.

33. Comparison of Photosynthesis and Respiration1
Comparison of Photosynthesis and Respiration
You can see that aerobic respiration is almost the reverse of photosynthesis.

34. Section Check 1
Question 1
This diagram shows that plants take in raw materials through their roots and leaves and get rid of wastes through _______.

35. A. neither their roots nor leaves B. their leaves only
Section Check 1
A. neither their roots nor leaves
B. their leaves only
C. their roots only
D. their roots and leaves also

36. Section Check 1
Answer
The correct answer is B. Plants take in carbon dioxide and oxygen through their leaves and water through their roots. They give off waste of water vapor, oxygen, and carbon dioxide through their leaves.

37. Section Check 1
Question 2
Why are stomata on leaves usually open during the day but shut at night?
Answer
Because photosynthesis is taking place mostly during the day, this is the time most plants need to take in raw materials. During the night, this process slows down.

38. Section Check 1
Question 3
What do plants produce during the process of photosynthesis?
Answer
Plants produce sugars (or glucose) and oxygen. The sugars produced are used by the plant for growth and energy. Most of the oxygen is given off as a waste.

39. What are plant responses?2
What are plant responses?
A stimulus is anything in the environment that causes a response in an organism. The response often involves movement either toward the stimulus or away from the stimulus.
A stimulus may come from outside (external) or inside (internal) the organism.

40. What are plant responses?2
What are plant responses?
Internal stimuli are usually chemicals produced by organisms.
Many of these chemicals are hormones. Hormones are substances made in one part of an organism for use somewhere else in the organism.

41. What are plant responses?2
What are plant responses?
Many different chemicals are known to act as hormones in plants.
Plants respond to external stimuli such as touch, light, and gravity.

42. What are plant responses?2
What are plant responses?
Some responses are rapid. Other plant responses are slower because they involve changes in growth.

43. Plant Responses 2
Tropisms
Some responses of a plant to an external stimuli are called tropisms.
A tropism (TROH pih zum) can be seen as movement caused by a change in growth and can be positive or negative.
For example, plants might grow toward a stimulusa positive tropismor away from a stimulusa negative tropism.

44. Plant Responses 2
Touch
One stimulus that can result in a change in a plant’s growth is touch.
When some plants touch a solid object, they respond by growing faster on one side of its stem than on the other side.
As a result the stem bends and twists around any object it touches.

45. Light 2 Light is an important stimulus to plants.
Plant Responses 2
Light
Light is an important stimulus to plants.
When a plant responds to light, the cells on the side of the plant opposite the light get longer than the cells facing the light.
Because of this uneven growth, the plant bends towards the light.

46. Plant Responses 2
Light
When a plant grows toward light it is called a positive response to light, or positive phototropism.

47. Plant Responses 2
Gravity
The downward growth of plant roots is a positive response to gravity.
A stem growing upward is a negative response to gravity.

48. Plant Responses 2
Plant Hormones
Hormones control the changes in growth that result from tropisms and affect other plant growth.

49. Plant Responses 2
Ethylene
Ethylene is produced in cells of ripening fruit, which stimulates the ripening process.

50. Plant Responses 2
Ethylene
Another plant response to ethylene causes a layer of cells to form between a leaf and the stem.
The cell layer causes the leaf to fall from the stem.

51. Plant Responses 2
Auxin
Auxin is a type of plant hormone that causes plant stems and leaves to exhibit positive response to light.

52. Plant Responses 2
Auxin
When light shines on a plant from one side, the auxin moves to the shaded side of the stem where it causes a change in growth.

53. Plant Responses 2
Auxin
Development of many parts of the plant, including flowers, roots, and fruit, is stimulated by auxins.
Because auxins are so important in plant development, synthetic auxins have been developed for use in agriculture.

54. Gibberellins and Cytokinins
Plant Responses 2
Gibberellins and Cytokinins
Gibberellins (jih buh REH lunz) are chemical substances that were isolated first from a fungus.
The fungus infects the stems of plants and causes them to grow too tall.

55. Gibberellins and Cytokinins
Plant Responses 2
Gibberellins and Cytokinins
Gibberellins can be mixed with water and sprayed on plants and seeds to stimulate plant stems to grow and seeds to germinate.

56. Gibberellins and Cytokinins
Plant Responses 2
Gibberellins and Cytokinins
Cytokinins (si tuh KI nunz) also cause rapid growth.
Cytokinins promote growth by causing faster cell divisions.
Like ethylene, the effect of cytokinins on the plant also is controlled by auxin.

57. Plant Responses 2
Abscisic Acid
Abscisic acid is the substance that keeps seeds from sprouting
and buds from developing during the winter.
This plant hormone also causes stomata to close and helps plants respond to water loss on hot summer days.

58. Plant Responses 2
Photoperiods
A plant’s response to the number of hours of daylight and darkness it receives daily is photoperiodism (foh toh PIHR ee uh dih zum).
The hours of daylight and darkness vary with the seasons.
These changes in lengths of daylight and darkness affect plant growth.

59. Plant Responses 2
Darkness and Flowers
Generally, plants that require less than 10 h to 12 h of darkness to flower are called long-day plants.

60. Plant Responses 2
Darkness and Flowers
Plants that need 12 or more hours of darkness to flower are called short-day plants.

61. Plant Responses 2
Day-Neutral Plants
Day-neutral plants have no specific photoperiod, and the flowering process can begin within a range of hours of darkness.
In nature, photoperiodism affects where flowering plants can grow and produce flowers and fruit.

62. Plant Responses 2
Day-Neutral Plants
This table shows how day length affects flowering in all three types of plants.

63. Question 1 2 Which is an example of negative gravitropism?
Section Check 2
Question 1
Which is an example of negative gravitropism?
A. plants coiling around things
B. plants leaning toward a window
C. roots growing downward
D. stems growing upward

64. Section Check 2
Answer
The correct answer is D. Plants growing upwards is a positive response to gravity while roots’ downward growth is a negative response to gravity.

65. Section Check 2
Question 2
Which plant hormone is responsible for the uneven growth illustrated in this diagram?

66. 2 A. abscisic acid B. auxin C. cytokinins D. gibberellins
Section Check 2
A. abscisic acid
B. auxin
C. cytokinins
D. gibberellins

67. Section Check 2
Answer
The answer is B. The hormone auxin causes this to occur. Auxin is more concentrated on the shaded side of the plant and causes the cells there to elongate. The plant then grows toward the light.

68. Section Check 2
Question 3
What are examples of three stimuli that cause tropisms in plants?

69. Section Check 2
Answer
Possible answers include: touch, light, gravity, electricity, temperature, and darkness. Tropisms are apparent movements of a plant that are caused by changes in growth. They can be positive or negative.

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