Photosynthesis

A is False and R is True.

Explanation
Photosynthesis only occurs in green parts of the plant. For example, roots and non-green tissues do not perform photosynthesis.
Chlorophyll is the pigment responsible for absorbing light energy from the sun, which is then used to drive the process of photosynthesis.

Both A and R are True.

Explanation
Guard cells are found in the lower portion of leaf and their function is to close and open the stomata as per need. They contain chloroplasts and carry out photosynthesis.

A is False and R is True.

Explanation
Palisade cells of mesophyll are loosely arranged towards the upper epidermis of a dorsiventral leaf. They along with spongy tissues are engaged in photosynthesis.

A is False and R is True.

Explanation
Phosphorylation, the process of adding a phosphate group to a molecule (like ADP to form ATP), occurs during both respiration and photosynthesis. In respiration, this process is called oxidative phosphorylation, while in photosynthesis, it is called photophosphorylation.

(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.

(a) The objective of given experiment is to show that sunlight is necessary for photosynthesis.

(b) The process shown here is 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.

(c) We destarch the leaves before experiment in order to remove the starch from leaves so that occurence of photosynthesis can be detected.

(d) To destarch the leaves the plant is kept in dark for 24-48 hours. This stops photosynthesis in the plant. During this time the starch already present in the leaves is translocated to storage organ of the plant fom the leaves.

(e) When we pour iodine solution over the bleached experimental leaf the area where starch is present turns blue.

(f) The equation for photosynthesis is given below:

$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{chlorophyll}]{\text{light energy}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2 \uparrow$

(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,

1. The leaf is boiled in water to kill the cells.
2. 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.

(a) Differences between light reaction and dark reaction (end products) —

(b) Differences between producers and consumers (organisms) —

(c) Differences between grass and grasshopper (mode of nutrition) —

(d) Differences between stoma and stroma (structure) —

1. Place some water plants (Elodea or Hydrilla) 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. (Ensure that the level of water in the beaker is above the level of stem of the inverted 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 flame which shows the presence of oxygen.

Light 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.

$2 H_2O \overset{\text{energy of 4 photons}}{\longrightarrow} 4H^+ + 4e^- + O_2$

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.

$NADP^+ + e^- + H ^+ \overset{\text{enzyme}}{\longrightarrow} NADPH$

The oxygen (O) component is given out as molecular oxygen (O₂).

$2O \longrightarrow O_2$

The electrons (e^-) are used in converting ADP (adenosine diphosphate) into energy rich compound ATP (adenosine triphosphate) by adding one phosphate group P_i (inorganic phosphate).

$ADP + P_i \text{ (inorganic phosphate)} \longrightarrow ATP$

This process is called photophosphorylation.

Dark reaction

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:

Thylakoid

Reason — Chlorophyll is located in the walls of thylakoid.

Carbon dioxide is evolved

Reason — In the process of photosynthesis, carbon dioxide is absorbed and oxygen is evolved as a by-product.

Green

Reason — The colour of any object is the light that is reflected by it. The chlorophyll reflects green colour and therefore it is green to our eyes.

Photon

Reason — The basic functional unit of solar energy is photon that is absorbed by the chlorophyll molecules and this leads to start of chain of reactions of photosynthesis.

Photolysis

Reason — The chlorophyll molecule absorbs solar energy and this energy is used to split the water molecule. This process ia called photolysis. (photo means light, lysis means disintegration)

Thylakoids

Reason — Stacked thylakoids are known as granum.

Methylated spirit

Reason — The leaf is boiled in Methylated spirit to remove chlorophyll.

Carbon dioxide

Reason — Carbon dioxide loses its oxygen or is reduced to form glucose. (loss of oxygen is reduction)

35°C

Reason — The rate of photosynthesis is maximum at 35°C and falls beyond it.

Polymerisation

Reason — Polymerisation is the process by which simple monomers (glucose) join to form complex polymers (starch).

(i) No
Corrected Statement — A few parts of a green plant like roots and flowers does not carry out photosynthesis as they lack chloroplasts and chlorophyll.

(ii) Yes

(iii) Yes

(iv) Yes

(v) Yes

(vi) No
Corrected Statement — Photosynthesis and transpiration go on side by side.

(vii) No
Corrected Statement — During sunlight, the guard cells turn turgid to open the stomata.

$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{chlorophyll}]{\text{light energy}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2 \uparrow$

Water

H₂O

The energy of Sun absorbed is used in splitting the water molecule into its two components (Hydrogen and Oxygen) and releasing electrons. This process is termed as photolysis.

The given reaction does not require light. It can occur during day as well as night. Therefore, it is known as Dark reaction.

The process of conversion of many simpler molecules into a complex, bigger molecule is termed as polymerisation. Several molecules of glucose join together to form a starch molecule.

The old term 'dark-phase' did not mean that it occurs when it is dark i.e. night. It only means that the reactions are not dependent on light. That is why, it is now better called as "light-independent phase".

(i) Large surface area of the leaf enables maximum light absorption by plant. Increased absorption of solar energy increases the Photosynthesis.

(ii) Thinness of the leaf reduces the distance between cells facilitating rapid transport of raw materials and translocation of food.

(iii) More numerous stomata allow rapid gaseous exchange and speed up the process of photosynthesis.

The three end products of photosynthesis are:

1. Glucose (C₆H₁₂O₆) — It is used in following four ways:
   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.
2. Water — can be reutilized in continuance of photosynthesis.
3. Oxygen — It is used in respiration in the leaf cells. Extra oxygen is released and diffused out in atmosphere.

Increasing carbon dioxide concentration increases rate of photosynthesis but it is stabilised at a particular point (upto 0.02% of CO₂ ) if there is no change in light intensity. If the light intensity is increased then increase in carbon dioxide concentration further increases the rate of photosynthesis and is again stabilised at 0.05% of CO₂.

In any experiment on photosynthesis, the presence of starch shows that the process of photosynthesis occurred. Therefore it is necessary to remove any pre-existing starch from the leaves. For destarching, the plant is kept for 24-48 hours in dark. It stops the synthesis of starch and the pre-existing starch, by then, is removed from leaves and is stored in storage organs.

We perform the iodine test to test the presence of starch.

Potassium hydroxide

The plants are called producers. They are the only organism with ability to convert the solar energy into chemical energy of the food. Therefore, all food chains start with a plant.

In terms of food chain, the honey bee is a consumer as it consumes plant nectar and derive its energy from nectar to carry out all the physiological processes. Honey produced by it is derived indirectly from plants. Therefore, Honey bee cannot be called as a producer.

(a) False
Corrected statement — Dark reaction of photosynthesis occurs simultaneously with light reaction.

(b) True

(c) False
Corrected statement — Green plants are producers.

(d) False
Corrected statement — Respiration results in loss of dry weight of the plants.

(e) False
Corrected statement — Photosynthesis stops at a temperature of about 40°C.

(f) True

(g) True

(h) True

(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 the 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.

(a) False
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) False
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) False
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) False
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) False
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) True

Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen.

(i) Grass → Grasshopper → Snake → Hawk

(ii) Corn → Mouse → Snake → Peacock

(a) Hydrilla, Elodea

(b) Geranium, Croton

(c) Carbon dioxide, water

(d) Light, Chlorophyll, Carbon dioxide and water

(e) Photo-chemical phase, Biosynthetic phase

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..

(a) Wall of thylakoid.

(b) Mesophyll cells of upper and lower epidermis of leaves.

(c) Chloroplast.

(d) Stomata.

(e) Beneath epidermis.

(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

(a) Food chain

(b) Hawk, Eagle

(c) Photosynthesis

(d) Oxygen

(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:

$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{chlorophyll}]{\text{light energy}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2 \uparrow$

(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:

(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.

Below diagram shows the stomatal apparatus found in the epidermis of leaves with all the different parts labelled:

(a) The main aim of the experiment is to show that oxygen is produced during photosynthesis.

(b) Oxygen is released from Water (H₂O).

(c) The gas present in the test tube makes a glowing splinter bursts into flames. This shows the presence of oxygen.

(d) Sodium Bicarbonate

(a) Autotrophs.

(b) Chloroplasts.

(c) ATP (Adenosine triphosphate).

(d) Glucose.

(e) The carbon dioxide dissolved in water.

(f) Stroma.

(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

(a) Plastid

(b) Chlorophyll

(c) Photosynthesis

(d) Thylakoids

(d) Stroma