Grade 7 Ch 10 Life processes in Plants

 

Chapter 10 Life Processes in Plants

Food gives nutrients- carbohydrates, fats, proteins, vitamins, minerals, water essential for growth.

Plants obtain nutrients differently than animals.

How Do Plants Grow?

Life span changes in plants due to growth & development:

→ new leaves & branches emerge

→ height increases

→ stem thickens

Activity: Testing Plant Growth

1. Take 3 pots (same soil) with saplings of chilli/tomato → A, B, C

2. Count leaves at start.

3. Pot A →direct sunlight + daily watering.

4. Pot B →direct sunlight + no water.

5. Pot C →darkness + daily watering.

6. After 2 weeks, record → height, number of leaves, leaf colour, other changes.

Observation (after 2 weeks):

Pot A → maximum growth - tall, more leaves, green.

Pot B → least growth - dried, leaves fell (may have died).

Pot C → little growth, weak, yellow.

Conclusion:

Plants need both sunlight + water for healthy growth.

Without water → plants dry.

Without sunlight → plants grow poorly, turn yellow.

How Do Plants Get Food for their Growth?

Animals get food from plants → directly (eat plants) or indirectly (eat plant-eating animals).

Plants do not eat food like animals.

Leaves: the 'food factories' of plants

Plants store food → as starch (a carbohydrate).

Starch is produced in leaves.

 Leaves are → broad, flat, green (chlorophyll).

Chlorophyll → captures sunlight efficiently.

Activity: Checking Starch in Leaves

1. Boil leaf in water (5 min) → it softens.

2. Dip it in test tube with alcohol.

3. Place test tube in beaker of boiling water → leaf becomes colourless.

4. Take leaf out in a plate.

5. Add diluted iodine solution → observe colour change.

                                                → blue-black colour = starch present

Caution → Alcohol flammable, don't heat near flame...

Conclusion → Green leaves make & store starch.

Activity: Starch in Green & Non-Green Parts

1. Take leaf with both green & non-green patches from 2 similar potted plants. One plant in sunlight,

    one in dark (36 hrs).

2. Sketch leaf patches to show locations of green & non-green areas.

3. Perform iodine test →compare colour.

Observation and Explanation:

Green patches (plant in sunlight) → turn blue-black

            → shows starch is produced, because chlorophyll + sunlight are present.

Green patches (plant in dark) no blue-black colour

            → starch not produced, because sunlight is absent and only chlorophyll is present.

Non-green patches (for both plants) no blue-black colour

             → little/no starch formed because chlorophyll is insufficient in non-green area.

Inference from Observations:

Leaves are green due to chlorophyll.

Chlorophyll helps prepare starch(food) in sunlight.

Starch is produced only in green patches of leaves.

Hence, leaves = 'food factories' of plants.

Role of air in the preparation of food

Activity: Role of Carbon dioxide

1. A green potted plant is kept in dark 2-3 days → it uses up stored starch (de-starched).

2. Select its leaf → half inserted into bottle with caustic soda (absorbs CO2), half outside.

3. Setup is kept in sunlight for few hours.

4. Leaf is tested for starch using iodine test.

Condition                                 Water  Sunlight           Chlorophyll      CO2     Starch present (Yes/No)

Part of leaf inside bottle         Yes       Yes                   Yes                   No        No

Part of leaf outside bottle       Yes       Yes                   Yes                   Yes       Yes

Observations:

Leaf part outside bottle → turns blue-black → so starch is formed.

Leaf part inside bottle → no blue-black colour → no starch formed.

Reason → Caustic soda removed CO2, so starch(food) is not made.

Conclusion → CO2 is essential for starch formation.

Learning from Activities:

Plants need → sunlight + water + chlorophyll + CO₂ to prepare food.

This process by which plants prepare food in the presence of sunlight and chlorophyll is called photosynthesis.

Leaf → main site of photosynthesis.

Other green parts (with chlorophyll) → can also perform photosynthesis.

Plants take in CO2 from air + water, use sunlight → prepare food. ess

Activity: Do Plants Release Something?

1. Setup A (sunlight) → bubbles in inverted test tube → oxygen released.

2. Setup B (dark) → no bubbles → no photosynthesis.

Conclusion →Plants release oxygen during photosynthesis.

Photosynthesis: in a nutshell.

Plants need water, sunlight, carbon dioxide, and chlorophyll to perform photosynthesis.

Photosynthesis produces carbohydrates

Food first formed → glucose (simple carbohydrate) - provides quick energy to plant

Extra glucose → stored as starch.

Word Equation: Sunlight

Carbon dioxide + Water  →   Glucose + Oxygen

Chlorophyll

How do leaves exchange gases during photosynthesis?

Plants need CO2 for photosynthesis and release 02.

Leaves main site of gas exchange.

Activity - Exchange of gases

1. Collect leaf (rhoeo/money plant/onion/hibiscus/coleus/grass).

2. Peel thin layer from lower surface.

3. Place peel on slide with water + ink.

4. Observe under microscope.

Observation → Tiny pores are visible - called stomata.

Conclusion → Stomata present on leaf surface allow exchange of gases (carbon dioxide in, oxygen out).

Transport in Plants

Transport of water and minerals

Plants need water for growth & photosynthesis.

Roots absorb water + minerals from soil

Minerals → essential nutrients for plant growth..

Activity: Water Transport

1 Take 2 tumblers → A (water), B (water + red ink)..

2 Cut 2 similar twigs' base obliquely underwater.

3. Place one twig in each tumbler → leave for 1 day.

Observations:

Plant in B → red colour is seen in stem, leaves, flowers

When non-immersed part of stem is cut → it shows red coloured pathways inside (seen with magnifying glass).

Explanation → How Ink Moves Upwards

Red colour travels upward through xylem (thin tube like structures in stem, branches, leaves)..

Xylem → transports water + minerals upward to leaves & other parts.

Transport of food

Leaves → primary site of photosynthesis & prepares food.

Food is transported to all parts via phloem (thin tubelike structures).

Food is also stored in seeds, roots & other parts.

Do Plants Respire?

All living things respire →  plants too.

Activity: Seeds Respire

1. Soak moong seeds → place on moist cotton in flask.

2. Close flask with cork having 2 holes → insert tubes A & B.

3. Keep this setup in dark for 24 hrs.

4. Connect flask's one tube to test tube with lime water using rubber pipe.

5. Keep another best tube with lime water unconnected.

Observation:

Connected best tube → lime water turned milky.

Unconnected test tube → no change

Where does this carbon dioxide come from?

Lime water turns milky with CO₂.

Air has small quantity of CO₂, but seeds released more CO₂ → shows seeds were respiring.

Respiration Process:

Glucose broken down with oxygen → releases CO₂, water, energy.

Energy is used for growth, development, life processes.

Word Equation: Glucose + Oxygen → CO₂ + Water + Energy

All plant parts (green/non-green) respire.

Conclusion:

Plants have systems to:

→Make food (photosynthesis)

→Transport food (xylem & phloem).

→Use food for energy (respiration)

 EXERCISE

Question 1. Complete the following table.

Answer:

Question 2. Imagine a situation where all the organisms that carry out photosynthesis on the earth have disappeared. What would be the impact of this on living organisms?

Answer: If all organisms that carry out photosynthesis disappeared, there would be no production of oxygen and food for other living organisms. This would disrupt the food chain, as plants provide food for herbivores and oxygen for respiration. Without plants, life on Earth would not be sustained.

Question 3. A potato slice shows the presence of starch with iodine solution. Where does the starch in potatoes come from? Where is the food synthesised in the plant, and how does it reach the potato?
Answer: The starch in potatoes comes from the glucose produced in the leaves during photosynthesis. Photosynthesis occurs in the leaves, where food is synthesised in the form of glucose. This glucose is then transported through the plant to the potato, where it is stored in the form of starch.

Question 4. Does the broad and flat structure of leaves make plants more efficient for photosynthesis? Justify your answer.
Answer: Yes, the broad and flat structure of leaves makes plants more efficient for photosynthesis. This shape increases the surface area, allowing more sunlight to be absorbed by the chlorophyll present in the leaves. It also helps in the exchange of gases through the stomata, thus enhancing the process of photosynthesis.

 

Question 5. X is broken down using Y to release carbon dioxide, Z, and energy.
                     X + Y → Carbon dioxide + Z + Energy
X, Y, and Z are three different components of the process. What do X, Y, and Z stand for?
Answer: X – Glucose     Y – Oxygen      Z – Water

Question 6. Krishna set-up an experiment with two potted plants of same size and placed one of them in sunlight and the other in a dark room, as shown in Fig. 10.11.

Fig. Experimental pots, (a) Sunlight (b) Complete dark

Answer the following questions.
(i) What idea might she be testing through this experiment?
Answer: Through this experiment, she is testing whether sunlight is necessary for photosynthesis in plants or not.

(ii) What are the visible differences in plants in both the conditions?
Answer: The plant kept in sunlight looks healthy and green as it performs photosynthesis while the plant kept in the dark room looks weak, pale, and yellowish because it cannot perform photosynthesis properly.

(iii) According to you, leaves of which plants confirm the iodine test for the presence of starch?
Answer: The leaves of the plant kept in sunlight will confirm the iodine test for starch.

Question 7.
Vani believes that ‘carbon dioxide is essential for photosynthesis’. She puts an experimental set-up, as shown in Fig. 10.11, to collect evidence to support or reject her idea.
                                  

(a) Sunlight with carbon dioxide
(b) Sunlight without carbon dioxide
(a) Dark with
(b) Dark without carbon dioxide carbon dioxide

Answer the following questions.
(i) In which plant(s) in the above set-up(s) will starch be formed?
Answer: Only in plant kept in sunlight with carbon dioxide, starch will be formed.

(ii) In which plant(s) in the above set-up(s) will starch not be formed?
Answer: In all plants except the plant kept in sunlight with carbon dioxide.

(iii) In which plant(s) in the above set-up(s) will oxygen be generated?
Answer: Oxygen will be generated in a plant kept in sunlight with carbon dioxide.

(iv) In which plant(s) in the above set-up(s) will oxygen not be generated?
Answer: Except for the plant kept in sunlight with carbon dioxide, oxygen will not be generated in any of the other plants.

Question 8. Ananya took four test tubes and filled three- fourth of each test tube with water. She labelled them A, B, C, and D (Fig. 10.12). In test tube A, she kept a snail; in test tube B, she kept a water plant; in test tube C, she kept both a snail and a plant. In test tube D, she kept only water. Ananya added a carbon dioxide indicator to all the test tubes. She recorded the initial colour of water and observed if there are any colour changes in the test tubes after 2-3 hours. What do you think she wants to find out? How will she know if she is correct?

                                                    Fig. Experimental set-up

Answer: Ananya wants to find out how plants and animals affect the amount of carbon dioxide in water. She is testing the role of respiration and photosynthesis. The carbon dioxide indicator changes colour depending on how much carbon dioxide is present in the water. Ananya will know she is correct by observing the colour changes in the carbon dioxide indicator in each test tube:

1. Test Tube A (Snail only): The indicator will turn yellow/orange, showing increased carbon dioxide due to the snail’s respiration.
2. Test Tube B (Plant only): The indicator will turn blue/purple, showing decreased carbon dioxide because the plant uses it during photosynthesis.
3. Test Tube C (Snail + Plant): The colour may stay neutral or slightly blue, showing a balance as the snail gives out carbon dioxide and the plant uses it.
4. Test Tube D (Only water): No colour change, as there is no living organism to add or remove carbon dioxide.

Question 9. Design an experiment to observe if water transportation in plants is quicker in warm or cold conditions.
Answer: To test whether water transportation in plants is quicker in warm or cold conditions, 

1. Take two identical potted plants. 
2. Place one plant in a warm location (near a heater or sunny spot) and the other plant in a cool place (like in the shade). 
3. Add a few drops of food colouring to the water and water both plants. 
4. After a few hours, observe the movement of the coloured water up the stem and into the leaves. 
5. The plant in the warm conditions will show faster movement of the coloured water, as higher temperatures increase the rate of evaporation and water transportation.

Question 10. Photosynthesis and respiration are essential to maintain balance in nature. Discuss.
Answer: Photosynthesis and respiration help maintain the balance of gases in nature. During photosynthesis, plants use sunlight, water, and carbon dioxide to make food and release oxygen. In respiration, plants and animals use oxygen to break down food for energy, releasing carbon dioxide. This exchange of gases keeps oxygen and carbon dioxide levels balanced, supporting life on Earth