Multiple Choice Type
(Select the most appropriate option in each case)
The production of starch, and not glucose, is often used as a measure of photosynthesis in leaves because
- starch is immediate product of photosynthesis
- glucose formed in photosynthesis soon gets converted into starch ✓
- starch is soluble in water
- sugar cannot be used
The number of water molecules required in the chemical reactions to produce one molecule of glucose during photosynthesis is
- twelve ✓
The rate of photosynthesis is not affected by
- light intensity
- humidity ✓
- CO2 concentration
Chlorophyll in a leaf is required for
- breaking down water into hydrogen and oxygen
- emitting green light
- trapping light energy ✓
- storing starch in the leaves
If the rate of respiration becomes more than the rate of photosynthesis, plants will:
- continue to live, but will not be able to store food ✓
- be killed instantly
- grow more vigorously because more energy will be available
- stop growing and die gradually of starvation
Which one chemical reaction occurs during photosynthesis?
- Carbon dioxide is reduced and water is oxidised ✓
- Water is reduced and carbon dioxide is oxidised
- Both carbon dioxide and water are oxidised
- Both carbon dioxide and water are reduced
The specific function of light energy in the process of photosynthesis is to
- reduce carbon dioxide
- synthesise glucose
- activate chlorophyll ✓
- split water molecule
A plant is kept in a dark cupboard for 48 hours before conducting any experiment on photosynthesis in order to
- remove chlorophyll from leaves
- remove starch from the leaves
- ensure that no photosynthesis occurred
- ensure that the leaves are free from starch ✓
During photosynthesis, the oxygen in glucose comes from
- CO2 ✓
- both CO2 and water
- oxygen via air
Very Short Answer Type
Name the following:
(a) The category of organisms that prepare their own food from basic raw materials.
(b) The kind of plastids found in the mesophyll cells of the leaf.
(c) The compound which stores energy in the cells.
(d) The first form of food substance produced during photosynthesis.
(e) The source of CO2 for aquatic plants.
(f) The part of chloroplast where the dark reaction of photosynthesis takes place.
(a) Producers or Autotrophs are the organisms that prepare their own food from basic raw materials.
(b) Chloroplasts is the kind of plastids found in the mesophyll cells of the leaf.
(c) ATP (Adenosine triphosphate) stores energy in the cells.
(d) Glucose is the first form of food substance produced during photosynthesis.
(e) The carbon dioxide dissolved in water.
(f) Stroma is the part of chloroplast where dark reaction of photosynthesis takes place.
Given below are groups of terms. In each group, the first pair indicates the relationship between the two terms. Complete the second pair accordingly.
(a) Chlorophyll : Magnesium :: Haemoglobin : …………………..
(b) Light reaction : Granum :: Dark reaction : …………………..
(c) Producers : Autotrophs :: Consumers : …………………..
(d) Respiration : Carbon dioxide :: Photosynthesis : …………………..
(e) Water and minerals : Xylem :: Prepared food : …………………..
(a) Chlorophyll : Magnesium :: Haemoglobin : Iron
(b) Light reaction : Granum :: Dark reaction : Stroma
(c) Producers : Autotrophs :: Consumers : Heterotrophs
(d) Respiration : Carbon dioxide :: Photosynthesis : Oxygen
(e) Water and minerals : Xylem :: Prepared food : Phloem
Short Answer Type
Identify the false statements and rewrite them correctly by changing the first or last word only.
(a) Dark reaction of photosynthesis occurs during night time.
Corrected statement — Dark reaction of photosynthesis occurs simultaneously with light reaction.
(b) Photosynthesis requires enzymes.
(c) Green plants are consumers.
Corrected statement — Green plants are producers.
(d) Photosynthesis results in loss of dry weight of the plants.
Corrected statement — Respiration results in loss of dry weight of the plants.
(e) Photosynthesis stops at a temperature of about 35°C.
Corrected statement — Photosynthesis stops at a temperature of about 40°C.
(f) Photosynthesis occurs only in cells containing chloroplasts.
(g) Green plants perform photosynthesis.
(h) Algae are autotrophs.
Fill in the blanks with the appropriate answer from the choices given in the brackets.
(a) The site of light reaction in the cells of a leaf is ............ (cytoplasm, stroma, grana).
(b) The chemical substance used to test the presence of starch in the cell of a leaf is ............. (CaCl2, iodine solution, Benedict solution).
(c) Stroma is ground substance in ................ (cytoplasm, chloroplast, ribosomes).
(d) The dark reaction of photosynthesis is known as .............. (Hill reaction, cyclic phosphorylation, Calvin cycle).
(e) In the flowering plants, food is transported in the form of .................. (sucrose, glucose, starch).
(a) The site of light reaction in the cells of a leaf is grana.
(b) The chemical substance used to test the presence of starch in the cell of a leaf is iodine solution.
(c) Stroma is ground substance in chloroplast.
(d) The dark reaction of photosynthesis is known as Calvin cycle.
(e) In the flowering plants, food is transported in the form of Sucrose.
Are the following statements true or false? Give reason in support of your answer.
(a) The rate of photosynthesis continues to rise as long as the intensity of light rises.
Corrected statement — Photosynthesis increases with the light intensity up to a certain limit only, and then it gets stabilised at the point S'(0.02% CO2).
(b) The outside atmospheric temperature has no effect on the rate of photosynthesis.
Corrected statement — The atmospheric temperature is an important external factor affecting photosynthesis. With the rise in temperature, the rate of photosynthesis rises. This rise occurs up to the optimum temperature of 35°C(maximum suitable temperature when the photosynthesis occurs best) after which the rate falls and stops above 40°C.
(c) If you immerse a leaf intact on the plant in ice cold water, it will continue to photosynthesise in bright sunshine.
Corrected statement — Ice cold water will hamper the process of photosynthesis in the immersed leaf, even if there is sufficient sunshine because the temperature is an important factor for the rate of photosynthesis.
(d) Destarching of the leaves of a potted plant can occur only at night.
Corrected statement — For destarching, the potted plant can be kept in a dark room for 24-48 hours. During this period, all the starch will be removed from the leaves and stored in the storage organs.
(e) If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will fail to occur.
Corrected statement — If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will continue to occur because the dark reaction is independent of light and it occurs simultaneously with the light dependent reaction.
(f) Photosynthesis is considered as a process supporting all life on earth.
Given below are five terms. Rewrite the terms in the correct order so as to be in logical sequence with regard to photosynthesis: (i) water molecules, (ii) oxygen, (iii) grana, (iv) hydrogen and hydroxyl ions, (v) photons.
Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen.
State any four differences between photosynthesis and respiration.
|Photosynthesis utilizes carbon dioxide and water in the presence of light to produce glucose and oxygen.||Respiration uses oxygen and glucose to power the activities of the cell.|
|Photosynthesis results in gain of dry weight of the plants.||Respiration results in loss of dry weight of the plants.|
|The raw materials for the photosynthesis are water, carbon dioxide and sunlight.||The raw material for respiration is glucose.|
|Photosynthesis occurs in plants and some photosynthetic bacteria.||Respiration occurs in all living organisms.|
Complete the following food chains by writing the names of appropriate organisms in the blanks:
(i) Grass → ............ → Snake → ...............
(ii) ........... → Mouse ............... → Peacock
(i) Grass → Grasshopper → Snake → Hawk
(ii) Corn → Mouse → Snake → Peacock
How do non-green plants such as fungi and bacteria obtain their nourishment?
Non-green plants such as fungi and bacteria obtain their nourishment from decaying organic matter in their environment. This matter comes from dead animals and plants. Fungi and bacteria break down the organic matter to obtain the nourishment and they release carbon dioxide back in the atmosphere.
All life owes its existence to chlorophyll. Give reason.
Chlorophyll is the green colouring matter found in plants. It is contained in microscopic cell organelles called chloroplasts. Chlorophyll is the foundation site for the photosynthesis in green plants. The initiation of photosynthesis takes place when the chlorophyll molecule traps the light energy. The light energy is then converted into chemical energy in the form of glucose using carbon dioxide (CO2) from the atmosphere, and water (H2O) from the soil. All other organisms, directly or indirectly depend on this food for their survival. The starting point of any food chain is always a plant. If green plants were to suddenly disappear, then so would virtually all life on Earth. Thus, we can say that all life owes its existence to chlorophyll.
Complete the following by filling the blanks 1 to 5 with appropriate words/ terms/ phrases:
To test the leaf for starch, the leaf is boiled in water to (1) …………… . It is next boiled in methylated spirit to (2) …………… . The leaf is placed in warm water to soften it. It is then placed in a dish and (3) ………… solution is added. The region, which contains starch, turns (4) …………… and the region, which does not contain starch, turns (5) ……………… .
To test the leaf for starch, the leaf is boiled in water to (1) kill the cells. It is next boiled in methylated spirit to (2) remove chlorophyll. The leaf is placed in warm water to soften it. It is then placed in a dish and (3) iodine solution is added. The region, which contains starch, turns (4) blue-black and the region, which does not contain starch, turns (5) brown.
"Oxygen is a waste product of photosynthesis." Comment.
Oxygen supports all life on earth. No living being can remain alive without oxygen. Some of the oxygen may be used in respiration in the leaf cells (the phenomenon is called photorespiration), but the major portion of it is not required and it diffuses out into the atmosphere through the stomata. However, in a sense, even this oxygen is not a waste because all organisms require it for their existence including the plants.
Define the following terms:
(d) Photolysis of water
(a) Photosynthesis — Photosynthesis 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 and release oxygen as a by-product.
(b) Thylakoids — Closely packed flattened sacs arranged in piles in the interior of chloroplasts are called Thylakoids.
(c) Chloroplast — Chloroplasts are minute oval bodies bounded by a double membrane which contains Thylakoids arranged in piles called Grana lying in a colourless ground substance called Stroma.
(d) Photolysis of water — Photolysis of water is defined as the splitting of H2O molecules into hydrogen ions and oxygen in the presence of light.
(e) Polymerisation — Polymerisation is the process in which several glucose molecules are transformed to produce one molecule of starch.
Photosynthesis in green plants is directly and indirectly dependent on so many plant structures. Explain briefly the role of the following structures in this process.
(a) Guard cells
(e) Xylem tissue in the leaf veins
(f) Phloem tissue in the leaf veins
(a) Guard cells — They are located in the leaf epidermis and pairs of guard cells surround and form stomatal pores. Guard cells use osmotic pressure to open and close stomata. And thus regulate the entry of carbon dioxide through the stomata.
(b) Cuticle — Cuticle is transparent and water proof to allow light to enter freely.
(c) Chlorophyll — Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light. Light energy is converted into chemical energy. With photosynthesis, chlorophyll absorbs energy and then transforms water and carbon dioxide into oxygen and carbohydrates.
(d) Stomata — The main function of Stomata is to let in carbon dioxide from the atmosphere for photosynthesis. Also most of the oxygen produced during photosynthesis diffuses out into the atmosphere through the stomata.
(e) Xylem tissue in the leaf Veins — Xylem cells mainly transport water and minerals from the roots to the leaves. Water is essential for photosynthesis to occur. Water is taken up by the roots from the soil, sent up through the stem and finally brought to the leaves (site of photosynthesis) through the xylem tissue. The water is then distributed in the mesophyll tissue.
(f) Phloem tissue in the leaf veins — The Pholem is composed of still living cells. Prepared food is transported from leaves to all parts of the plant by the phloem tissue. The glucose is converted into insoluble starch and later into soluble sugar sucrose, which is transported in solution through the phloem in the veins of the leaf and down through the phloem of the stem.
(a) It is necessary to place a plant in the dark before starting an experiment on photosynthesis.
(b) It is not possible to demonstrate respiration in a green plant kept in sunlight.
(c) Most leaves have the upper surface more green and shiny than the lower surface.
(d) During the starch test, the leaf is -
- boiled in water.
- boiled in methylated spirit.
(a) A plant used for experiments on photosynthesis should initially be placed in the dark for 24 to 48 hours to destarch the leaves. During this period, all the starch will be removed from the leaves and stored in the storage organs. The leaves will not show the presence of starch. So the various experiments on photosynthesis can be carried out effectively.
(b) If a green plant is kept in bright light, it tends to use up all the CO2 produced during respiration, for photosynthesis. Thus, the release of CO2 cannot be demonstrated. Hence, it is difficult to demonstrate respiration as these two processes occur simultaneously.
(c) Due to more amount of chlorophyll on the upper surface more light is trapped. The chloroplasts are concentrated in the upper layers of the leaf which helps cells to trap the sunlight quickly. The upper surface is more green and shiny because it has a waxy coating to prevent loss of water due to evaporation.
(d) During the starch test,
- The leaf is boiled in water to kill the cells.
- The leaf is boiled in methylated spirit till it becomes pale-white due to the removal of chlorophyll. The leaf now becomes hard and brittle.
Distinguish between the following pairs on the basis of words indicated in the brackets ( )
(a) Light reaction and Dark reaction (end products)
(b) Producers and Consumers (organisms)
(c) Grass and Grasshopper (mode of nutrition)
(d) Stoma and Stroma (structure)
(a) Differences between light reaction and dark reaction (end products) —
|Light Reaction||Dark Reaction|
|ATP and NADPH are the end products of this reaction.||Glucose is the main product formed during dark reaction.|
|The water molecule split into hydrogen and oxygen.||No splitting of water.|
(b) Differences between producers and consumers (organisms) —
|They are autotrophs.||They are heterotrophs.|
|They can convert inorganic substances into organic substances.||They cannot convert inorganic substances into organic substances.|
|It includes green plants and photosynthetic micro-organisms.||It includes herbivores and carnivores.|
|For example — green plants||For example — Animals|
(c) Differences between grass and grasshopper (mode of nutrition) —
|Green grass being a producer is capable of producing its own food by photosynthesis.||Grasshopper is a primary consumer (herbivore) and directly feeds on producers like grass.|
(d) Differences between stoma and stroma (structure) —
|A stoma is a microscopic pore surrounded by two specialized guard cells found in the leaves and stems. Its main function is gaseous exchange.||Stroma is the colourless ground substance found in the chloroplast. It is the site of the light independent reactions of photosynthesis.|
How would you demonstrate that green plants release oxygen when exposed to light?
- Place some water plants (Elodea or Hydrilla) in a beaker containing pond water and cover them by a short-stemmed funnel.
- Invert a test-tube full of water over the stem of the funnel. (Ensure that the level of water in the beaker is above the level of stem of the inverted funnel).
- Place the apparatus in the sun for a few hours. Bubbles of the gas will collect in the test-tube.
- Test the gas in the test-tube. A glowing splinter bursts into flame which shows the presence of oxygen.
Describe the main chemical changes which occur during photosynthesis in
- Light reaction
- Dark reaction
The light reaction occurs in two main steps:
Step 1 — Activation of chlorophyll
The chlorophyll on exposure to light energy becomes activated by absorbing photons.
Step 2 — Splitting of Water
The absorbed energy is used in splitting the water molecule (H2O) into its two components (Hydrogen and Oxygen) and releasing electrons.
This reaction is known as photolysis of water.
End result of the products of photolysis
The hydrogen ions (H+) are picked up by a compound NADP (Nicotinamide adenine dinucleotide phosphate) to form NADPH.
The oxygen (O) component is given out as molecular oxygen (O2).
The electrons (e-) are used in converting ADP (adenosine diphosphate) into energy rich compound ATP (adenosine triphosphate) by adding one phosphate group Pi (inorganic phosphate).
This process is called photophosphorylation.
The reactions in this phase do not require light energy and occur simultaneously with the light reaction. The time gap between the light and dark reaction is less than one thousandth of a second. In the dark reaction, ATP and NADPH molecules (produced during light reaction) are used to produce glucose (C6H12O6) from carbon dioxide. Fixation and reduction of carbon dioxide occurs in the stroma of the chloroplast through a series of reactions. The glucose produced is either immediately used up by the cells or stored in the form of starch.
Below is the summary of events in Light reaction and Light independent reactions of photosynthesis:
Structured / Application / Skill Type
Given below is a schematic diagram to illustrate some aspects of photosynthesis.
(a) Fill up the gaps, in blank spaces (1-4), by writing the names of the correct items.
(b) What phenomenon do the thick arrows A and B indicate?
(a) Blank spaces (1-4) are labelled below:
- 1 → Sunlight
- 2 → Oxygen
- 3 → Glucose
- 4 → Xylem
(b) Phenomena represented by thick arrows A and B are:
- A → Transpiration
- B → Translocation
Given below is the representation of a certain phenomenon in nature with four organisms 1-4.
(a) Name the phenomenon represented.
(b) Name any one organism that could be shown at No .5
(c) Name the biological process which was the starting point of the whole chain.
(d) Name one natural element which all the organisms 2-4 and even 5 are getting from No. 1 for their survival.
(a) Food chain
(b) Hawk, Eagle
A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagram and answer the questions:
(a) What aspect of photosynthesis is being tested in the above diagram?
(b) Why was the plant placed in the dark before beginning the experiment?
(c) Write a balanced chemical equation to represent the process of photosynthesis.
(d) What will be the result of starch test when performed on leaf A shown in the diagram?
(e) Draw a neat and labelled diagram of a chloroplast.
(a) The above experiment is conducted to show that chlorophyll is necessary for photosynthesis.
(b) The plant was placed in the dark before beginning the experiment to destarch the leaves.
(c) Balanced chemical equation representing the process of photosynthesis is given below:
(d) After the starch test on leaf A, only the green parts of the leaf turn bluish, showing the presence of starch.
(e) Below diagram shows Chloroplast with its different parts labelled:
Given below is the diagram of an experimental set-up:
a. What is the objective of this experiment?
b. Will it work satisfactorily? Given reason.
c. What alteration (s) will you make in it for obtaining expected result?
d. Would you take any step before starting the experiment? Describe this step and explain its necessity.
(a) The objective is to prove that carbon dioxide is necessary for photosynthesis.
(b) No, the experiment will not work satisfactorily because, the beaker contains lime water which does not absorb CO2
(c) To obtain expected result replace the lime water from potassium hydroxide because it absorbs carbon dioxide.
(d) Before starting the experiment, it is necessary to destarch the leaves of the plant by keeping the plant in complete darkness for 48 hours. This is because if the plant is not destarched, then the experiment will give false results because starch stored previously may be detected in the leaf placed in the beaker even if no starch is produced during the experiment.
Draw a neat diagram of the stomatal apparatus found in the epidermis of leaves and label the Stoma, Guard cells, Chloroplast, Epidermal cells, Cell wall and Nucleus.
Below diagram shows the stomatal apparatus found in the epidermis of leaves with all the different parts labelled:
The diagram below shows two test-tubes A and B. Test-tube A contains a green water plant. Test-tube B contains both a green water plant and a snail. Both test-tubes are kept in sunlight. Answer the questions that follow:
(a) Name the physiological process that releases the bubbles of oxygen.
(b) Explain the physiological process as mentioned above in (a).
(c) What is the purpose of keeping a snail in test-tube B?
(d) Why does test-tube 'B' have more bubbles of oxygen?
(e) Give an example of a water plant that can be used in the above experiment.
(a) Photosynthesis releases bubbles of oxygen.
(b) Photosynthesis is a physiological process by which plant cells containing chlorophyll produce food in the form of carbohydrates by using carbon dioxide, water and light energy. Oxygen is released as a by-product.
(c) The purpose of keeping a snail in test-tube 'B' is to increase the rate of photosynthesis by increasing the concentration of carbon dioxide.
(d) The plant in test tube B has more concentration of CO2 available because the snail releases CO2 during respiration. This increases the rate of photosynthesis in the plant placed in test tube B which leads to the release of more amount of oxygen.
(e) Elodea or Hydrilla.