Photosynthesis Flashcards
1
Q
Why is photosynthesis the most significant life process?
A
It provides food not only to the plant itself but to all animal life including humans, and also the life supporting oxygen gas in the atmosphere for breathing
2
Q
What is photsynthesis?
A
It is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch), from carbon dioxide and water, by using light energy. Plants release oxygen as a by product during photosynthesis.
3
Q
Give the importance of photosynthesis
A
- Food for all
2. Oxygen to breathe in
4
Q
How does photosynthesis support all life on earth?
A
It is the only biological process which releases oxygen into the atmosphere. No living being can remain alive without oxygen
5
Q
What is chlorophyll?
A
It is the green pigment found in plants. It is a highly complex substance, composed of carbon, oxygen, hydrogen, magnesium and nitrogen
6
Q
Where is chlorophyll found?
A
It is contained in microscopic cell organelles called chloroplasts
7
Q
What are chloroplasts?
A
They are minute oval bodies bounded by a double membrane, and their interior contains thylakoids arranged in grana lying in the stroma
8
Q
What are thylakoids?
A
Closely packed flattened sacs
9
Q
What is a granum?
A
A pile of thylakoids
10
Q
What is stroma?
A
Colourless ground substance present in the chloroplasts in which the thylakoids lie
11
Q
How many chloroplasts are normally found in a cell?
A
40-50
12
Q
Where is the pigment chlorophyll contained?
A
In the walls of thylakoids
13
Q
Where are chloroplasts contained?
A
- In the mesophyll cells located between the upper epidermis and the lower epidermis - in the palisade cells and spongy cells - of leaves
- In the guard cells of stomata
- In the outer layers of young green stems
14
Q
What are frets?
A
Bars connecting the grana (Interconnecting bars)
15
Q
How many chloroplasts are there per sq. mm. of leaf surface?
A
500,000
16
Q
How many types of chlorophyll are there?
A
9 types
17
Q
Name the best known and most abundant types of chlorophyll
A
- chlorophyll-a
2. chlorophyll-b
18
Q
Why does chlorophyll appear green?
A
Chlorophylls absorb light at both ends of the visible spectrum - i.e. BLUE and RED light, and reflect away the green light
19
Q
Which lights are most effective for photosynthesis?
A
Blue and red lights
20
Q
What does the formation of chlorophyll depend on?
A
On the exposure of the plant to light
21
Q
Why does the grass growing in the shade under a stone turn yellowish?
A
Due to the non-formation of new chlorophyll and due to the disintegration of the older one in the absence of light
22
Q
What are stomata?
A
They are minute openings occurring in large numbers on the lower surface of the leaf
23
Q
What is the main function of stomata?
A
To let in carbon dioxide from the atmosphere for photsynthesis
24
Q
Are transpiration and photosynthesis simultaneous processes?
A
Yes
25
What happens to the stomata when it is light vs dark?
Stomata tend to close their openings when it is dark so that water loss is minimised from leaves through transpiration. When there is light, they reopen to allow CO2 to diffuse in
26
What is said to be the price that the plant pays for photosynthesis?
Transpiration
27
What is the closing and opening of the stomata on account of?
On account of the movement of water in and out of the guard cells
28
Name the modifications in the guard cells that permit photosynthesis
1. Thich inner wall facing the opening and a thin outer wall on the opposite side
2. Their cytoplasm contains chloroplasts
29
Name the two theories about the opening and closing of stomata
1. Potassium ion concentration theory
| 2. Sugar concentration theory
30
According the K+ ion concentration theory, what does the stomatal opening and closing depend on?
On the generation of potassium ion (K+) gradient
31
Describe the stomatal opening and closing according to the K+ ion concentration theory
1. During daytime, the chloroplasts in the guard cells photosynthesise which leads to the production of ATP
2. This ATP is used to actively pump K+ ions from the adjacent cells into the guard cells
3. Increased K+ concentration in the guard cells makes them hypertonic, and thus, they draw more water in from the adjacent cells and become turgid, resulting in them moving outwards to open the stomatal pore
4. At night, the K+ ions leak out thus reducing the turgor of guard cells and the stomatal opening closes
32
When do the stomata close?
If for any reason, the water content of the leaf is falling short, the water is drawn out of the guard cells due to exosmosis making them flaccid. As a result, their inner thick walls straighten to close the stomata
33
What are the principal centres of photosynthesis?
Mesophyll cells (palisade and spongy)
34
How is light energy trapped for photosynthesis?
During daytime, when sunlight falls on the leaf, the light energy is trapped by the chlorophyll of the upper layers of mesophyll, especially the palisade cells
35
What is the light energy trapped utilized in?
In chemical processes involving the manufacture of food, where the raw materials used are carbon dioxide and water
36
How does carbon dioxide enter the leaf for photosynthesis?
By diffusion down a concentration gradient (higher conc. outside the leaf than inside) through the stomata
37
Give the chemical equation to represent photosynthesis?
6CO2 + 12H2O -> C6H12O6 + 6H2O + 6O2 ↑
38
Comment on the 6 molecules of water liberated at the end of photosynthesis
They are the ones that are re-formed during a chain of reactions and not out of the original ones
39
Name the two phases of photosynthesis
1. Light-dependent phase
| 2. Light-independent phase
40
Why is the light-dependent phase called the photochemical phase?
A series of chemical reactions occur in very quick succession. initiated by light and therefore, the phase is called the photochemical phase
41
Where does the light reaction take place?
In the thylakoids (containing chlorophyll) of the chloroplasts
42
Name the two main steps of the light-dependent phase
1. Activation of chlorophyll
| 2. Splitting of water
43
How does chlorophyll become activated in the photochemical phase?
On exposure to light energy, chlorophyll gets activated by absorbing photons
44
What are photons?
The smallest units of light energy
45
Give the chemical equation representing the splitting of water
2H2O (energy of 4 photons) -> 4H+ + 4e- + O2
46
What is photolysis?
The splitting of the water molecules into hydrogen ions and oxygen in the presence of light
47
What is the meaning of the term photolysis?
photo: light, lysis: breaking - splitting by light
48
Where does photolysis occur?
In the grana of the chloroplast
49
What happens to the hydrogen ions formed at the end of photolysis?
The hydrogen ions (H+) are picked up by a compound Nicotinamide adenine dinucleotide phosphate (NADP) to form NADPH
50
Give the equation for the formation of NADPH
NADP+ + e- + H+ (enzymes)-> NADPH
51
What happens to the oxygen component formed at the end of photolysis?
It is given out as molecular oxygen O2
| 2O -> O2
52
What happens to the electrons formed at the end of photolysis?
The electrons are used in converting ADP (adenosine diphosphate) into energy-rich compound ATP by adding one phosphate group P▼i (inorganic phosphate)
53
Give the equation for formation of ATP
ADP + P▼i -> ATP
54
What is phosphorylation?
Addition of inorganic phosphate to the compound ADP to from the energy-rich compound ATP
55
What is photophosphorylation?
Addition of inorganic phosphate to the compound ADP to from the energy-rich compound ATP by using the energy that comes from photons
56
Give another name for light-independent phase
Biosynthetic phase
57
What is the time gap between the light-dependent and independent phase?
Less than even one-thousandth of a second
58
What is glucose converted into as soon as it is formed?
Starch
59
What is polymerisation?
The process of several glucose molecules being transformed to produce one molecule of starch
60
Name the substances that plant change glucose into
1. Starch
2. Sucrose (cane sugar)
3. Oils
61
What is cane sugar chemically called?
Disaccharide or double sugar
62
Where do light-independent reactions occur?
In the stroma of the chloroplast
63
What is the source of the oxygen released in photosynthesis?
Water
64
Name the adaptations in a leaf to perform photosynthesis?
1. Large surface area
2. Leaf arrangement at the right angle
3. Cuticle + upper epidermis - transparent & water proof
4. Numerous stomata
5. The thinness of leaves
6. The chloroplasts concentrated in upper layers
7. Extensive vein system
65
How does large surface area facilitate photosynthesis?
Large surface area allows maximum light absorption
66
How does leaf arrangement facilitate photosynthesis?
Leaf arrangement at the right angle to the light source to obtain maximum light
67
What is the adaptation in cuticle and upper epidermis that facilitates photosynthesis?
They are transparent and water proof to allow light to enter freely
68
How does the presence of numerous stomata help in photosynthesis?
They allow rapid exchange of gases (O2 and CO2)
69
What is the need for narrowing of leaves in certain plants?
Minimising transpiration in order to conserve water
70
Name some plants which have narrow leaves
Oleander and pine
71
How does the thinness of leaves help in photosynthesis?
It reduces the distance between cells facilitating rapid transport
72
How does extensive vein system help in photosynthesis?
Helps in rapid transport to and from the mesophyll cells
73
What are the three end products of photosynthesis?
1. Glucose
2. Water
3. Oxygen
74
How is simple sugar glucose at the end of photosynthesis used by the plant?
1. Immediately consumed by the plant cells
2. Stored in the form of insoluble starch
3. Converted into sucrose
4. Used in synthesizing fats, proteins, etc
75
How is the water produced at the end of photosynthesis used by the plant?
It may be re-utilized in the continuance of photosynthesis
76
How is the oxygen produced at the end of photosynthesis used by the plant?
1. Some of it is used in respiration in the leaf cells
2. Diffuses out into the atmosphere through stomata
3. Plants require it at night
77
What is photorespiration?
Respiration in the leaf cells using oxygen
78
Why is glucose converted into insoluble starch for temporary storage in the leaf?
The glucose is formed in the leaf very rapidly during photosynthesis and it cannot be transported to the other parts with the same rapidity
79
What happens to the stored insoluble starch at night?
It is reconverted into insoluble sugar which is transported in solution through the veins of the leaf and down the phloem of the stem
80
What is the process of conversion and reconversion of glucose in potato?
Glucose is converted into insoluble starch for temporary storage in the leaf. At night, the starch is reconverted into soluble sugar which is translocated to different parts of the plant where it may be reconverted into starch for storage to produce energy for various functions in the plant
81
Name the external factors affecting photosynthesis
1. Light intensity
2. Carbon dioxide
3. Temperature
4. Water content
82
How do light intensity and carbon dioxide concentration affect photosynthesis?
Photosynthesis increases with light intensity up to a certain limit only, and then it gets stabilised at 0.02% CO2 conc. But if, at this point, the CO2 concentration is increased, the photosynthesis also increases further and again gets stabilised at 0.05% CO2 for the two factors together
83
How does temperature affect photosynthesis?
With the rise in temperature, the rate of photosynthesis rises. This rise occurs up to the optimum temperature of 35 C after which the rate falls and stops above 40 C
84
What is the optimum temperature range for photosynthesis?
25-30 C
85
What is the maximum suitable temperature when photosynthesis occurs best?
35 C
86
What is the effect of a rise of 10 C up to the optimum temperature?
The rate of photosynthesis is doubled
87
How does water content affect photosynthesis?
The scarcity of water due to reduced absorption from the soil or due to an excessive loss through transpiration reduces the rate of photosynthesis by reducing diffusive capacity (CO2 intake) due to the closure of stomata
88
How much water absorbed by the root is utilised in photosynthesis?
Only 1%
89
Name the internal factors affecting photosynthesis
1. Chlorophyll
2. Protoplasm
3. Structure of a leaf
4. Accumulation of carbohydrates
90
How does chlorophyll affect photosynthesis?
Nutritional deficiencies of minerals cause loss of chlorophyll, and hence the drop in trapping solar energy
91
How does protoplasm affect photosynthesis?
Dehydration of protoplasm for some reason reduces the rate of photosynthesis
92
The accumulation of which carbohydrates reduces the rate of photosynthesis?
Sugar and starch
93
How does the structure of leaf affect photosynthesis?
The thickness of cuticle, the distribution of stomata and the size of the leaf influence the amount of light and the amount of CO2 entering the leaf
94
What is the trend in the rate of photosynthesis in 24 hours?
The rate of photosynthesis increases from dawn to midday and declines as dusk approaches
95
Comment on photosynthesis and respiration in plants during day and night
In light, the effects of the respiratory activity of plants are masked by those of photosynthesis and there is a net output of oxygen. In darkness, respiration alone is responsible for changes in the gaseous composition of a plant's surrounding atmosphere
96
Which process is responsible for changes in the gaseous composition of a plant's surrounding atmosphere at night?
Respiration
97
In which plants does photosynthesis at night occur?
Aloe vera, Tulsi, Neem, Peepal, epiphytes, desert plants
98
How does photosynthesis occur at night for some plants?
Some desert plants and epiphytes are able to release oxygen even during the night as they perform photosynthesis using a different pathway called the CAM pathway
99
What is a destarched plant?
One whose leaves are free from starch
100
Why should a plant used for experiments on photosynthesis be placed in the dark for 2-3 days?
To destarch the leaves. During this period, all the starch will be removed from the leaves and stored in the storage organs.
101
Give the steps to test a leaf for starch
1. Dip the leaf in boiling water for a minute to kill the cells
2. Boil the leaf in methylated spirit over a water bath till it becomes pale white due to the removal of chlorophyll
3. Place it again in hot water to soften it
4. Spread the leaf in a dish and pour iodine solution on it
102
What happens to the leaf after boiling it in methylated spirit over a water bath?
It loses all chlorophyll and becomes hard and brittle
103
How is the presence of starch indicated?
By a blue-black color. A leaf without starch will show brown coloration.
104
What is the composition of iodine solution?
Iodine = 0.3g; Potassium iodide = 1.5g; Water = 100 ml
105
Which plant do you take in an experiment to show that chlorophyll is necessary for photosynthesis?
A plant with variegated leaves having some green and non-green areas. Coleus, Geranium and Croton
106
Give the steps of an experiment to show that chlorophyll is necessary for photosynthesis
1. Destarch the leaves by keeping the plant in a dark room for a few days
2. Place the plant in the sun. After a few hours, pluck a leaf
3. Make its outline on paper and mark the green and non-green areas on the outline
4. Test the leaf for starch. Only the green parts of the leaf turn bluish
107
Give the steps of an experiment to show that sunlight is necessary for photosynthesis
1. Take a plant with destarched leaves
2. Cover one of its leaves with black paper on which a design is cut
3. Place this plant in the sun
4. After a few hours, test the leaf which is covered by black paper for the presence of starch
5. Only the exposed parts of the leaf turn blue black
108
Give the steps of an experiment to show that carbon dioxide is necessary for photosynthesis
1. Take a plant with destarched leaves
2. Take a part of one of its leaves through a split cork into a conical flask containing potassium hydroxide
3. Leave the plant in sunlight
4. After a few hours, test the leaf for starch
5. The part of the leaf exposed to the atmospheric air becomes blue-black, and the part inside the flask containing KOH doesn't become blue black
109
Why is KOH used in the experiment showing that carbon dioxide is necessary for photosynthesis?
It absorbs carbon dioxide
110
Give the steps of an experiment to show that oxygen is produced during photosynthesis
1. Place some water plants in a beaker containing pond water and cover them by a short-stemmed funnel
2. Invert a test tube full of water over the stem of the funnel
3. Place the apparatus in the sun for a few hours. Bubbles of the gas will collect in the test tube
4. Test the gas in the test tube. A glowing splinter bursts into flames which shows the presence of oxygen
111
What are the precautions in the hydrilla plant experiment?
Ensure that the level of of water in the beaker is above the stem of the inverted funnel
112
Which plants are taken in the experiment demonstrating the production of oxygen in photosynthesis?
Hydrilla or Elodea
113
What is the food chain?
The chain of food dependence of herbivores on plants and carnivores on herbivores is called the food chain
114
What is the starting point of a food chain?
A producer (plant)
115
How do non-green plants like fungi and bacteria obtain their nourishment?
From decaying matter in their environment. This matter comes from dead animals and plants, which in their own turn were dependent on photosynthesis
116
What is the carbon cycle?
It is a series of chemical reactions in which carbon as a chemical element is removed from the air, used by living organisms in their body processes and is finally returned to air
117
Name the essential steps in the carbon cycle
1. Photosynthesis (in green plants)
2. Entering into the food chain from herbivores to carnivores
3. Respiration (Plants and animals)
4. Decaying dead plants and animal remains by decomposers
5. Burning of organic fuels - wood, coal, petroleum etc
6. Heating of limestone in lime kilns.
118
What is the percentage of carbon dioxide in air?
0.03%
119
How does carbon dioxide end up in the ocean?
It diffuses into water becoming carbonates and bicarbonates in oceans
120
How does carbon dioxide end up in limestone?
Carbon dioxide is found in oceans in the form of carbonates and bicarbonates, and therefore in rock and coral shells which form limestones
121
What else are plants called because they provide self nutrition?
Autotrophs
122
What occurs in the light independent reaction?
Transfer of hydrogen from NADPH through a series of chemical reactions to combine with CO2 to produce C6H12O6 by using energy from ATP
123
What is the immediate product of photosynthesis?
Glucose
124
What are the by-products of photosynthesis?
Water and oxygen
125
Which chemical reaction occurs with reference to reduction and oxidation in photosynthesis?
Carbon dioxide is reduced and water is oxidised
126
During photosynthesis, from where does the oxygen in glucose come?
From carbon dioxide
127
Which process results in loss of dry weight of the plants?
Respiration
128
The dark reaction of photosynthesis is known as?
Calvin cycle
129
In flowering plants, in which form is food transported?
Sucrose
130
What would the laborers be for chloroplasts?
Enzymes
