GSEB Class 7 Science Solutions Chapter 1 Nutrition in Plants

Question 1. Why do organisms take food?
Answer: Food is required by all organisms for many different purposes:

• The primary purpose of food is to assist in the body's growth and development.
• Food gives energy for daily activities like running, walking, or lifting our arms.
• Food is also essential for replacing and repairing injured parts of the body.
• Food helps us build immunity to battle illnesses and keeps us safe from infections.

Exam Tip: When answering about the purpose of food, remember to cover its roles in growth, energy, repair, and protection against disease.

Question 2. Distinguish between a parasite and a saprotroph?
Answer:

Parasite:

• Parasites get their nourishment from a living organism.
• The creature it feeds on is known as the host.
• A parasite gets pre-made food from the living being it feeds upon.

Saprotrophs:

• They get food from dead and decaying organisms.
• They do not consume living organisms for sustenance.
• They release digestive liquids onto the material they live on, turning it into a liquid which they then absorb.

Exam Tip: For distinctions, clearly state the key differences like the source of food (living vs. dead matter) and the method of obtaining nutrition for each type of organism.

Question 3. How would you test the presence of starch in leaves?
Answer: We can check for starch in leaves using an Iodine test. First, we get rid of the green pigment (chlorophyll) by boiling the leaf in alcohol. After that, when we add two drops of iodine solution, if starch is present, the leaf's color will turn blue-black.
In simple words: To find starch in leaves, do an iodine test. Remove chlorophyll with alcohol, then add iodine. If it turns blue-black, starch is there.

Exam Tip: Remember the key steps: removal of chlorophyll (alcohol boiling), followed by the application of iodine solution, and the resulting blue-black color change indicating starch presence.

Question 4. Give a brief description of the process of synthesis of food in green plants.
Answer: Green plants possess chlorophyll within their leaves. These leaves utilize carbon dioxide and water to create food when sunlight is available. This process is called photosynthesis.
\( \text{Carbon dioxide} + \text{Water} \xrightarrow{\text{Sunlight, Chlorophyll}} \text{Carbohydrate (glucose)} + \text{Oxygen} \)
Oxygen is set free during the process of photosynthesis.
In simple words: Green plants make their own food in their leaves. They use sunlight, water, and carbon dioxide. This makes sugar for food and releases oxygen.

Exam Tip: When describing photosynthesis, always include the raw materials (carbon dioxide, water, sunlight) and the products (carbohydrate/glucose, oxygen), along with the role of chlorophyll.

Question 5. Show with the help of a sketch that plants are the ultimate source of food.
Answer: Plants are producers that convert solar energy into chemical energy, forming the base of all food chains. All other organisms depend on plants directly or indirectly for their food.
This sketch demonstrates how plants are the primary source of food for nearly all life forms:

Exam Tip: A food chain diagram should always start with the sun's energy, followed by producers (plants), then various levels of consumers (herbivores, carnivores), and finally decomposers, illustrating the flow of energy.

Question 6. Fill in the blanks:
(a) Green plants are called \_\_\_\_\_\_\_ since they synthesise their own food.
(b) The food synthesised by plants is stored as \_\_\_\_\_\_\_.
(c) In photosynthesis solar energy is absorbed by the pigment called \_\_\_\_\_\_\_.
(d) During photosynthesis plants take in \_\_\_\_\_\_\_ and release \_\_\_\_\_\_\_ gas.
Answer:
(a) autotrophs
(b) starch
(c) chlorophyll
(d) carbon dioxide, oxygen
In simple words: Plants make their food so they are 'autotrophs'. They save this food as 'starch'. For photosynthesis, they use 'chlorophyll' to catch sunlight, taking in 'carbon dioxide' and giving out 'oxygen'.

Exam Tip: Memorize these key terms related to plant nutrition: autotrophs (self-feeders), starch (stored food), chlorophyll (light-absorbing pigment), and the gases exchanged during photosynthesis (carbon dioxide in, oxygen out).

Question 7. Name the following:
(i) A parasitic plant with yellow, slender and branched stem.
(ii) A plant that is partially autotrophic.
(iii) The pores through which leaves exchange gases.
Answer:
(i) Cuscuta
(ii) Insectivorous plant or Pitcher Plant
(iii) Stomata
In simple words: We learned about Cuscuta, an insectivorous plant (like a pitcher plant), and stomata. Each has a special job in the plant world.

Exam Tip: Understand the unique characteristics of different plant types: parasitic (Cuscuta), partially autotrophic (insectivorous plants), and the role of stomata in gas exchange.

Question 8. Tick the correct answer:
(a) Cuscuta is an example of:
(i) autotroph
(ii) parasite
(iii) saprotroph
(iv) host
Answer: (ii) parasite
In simple words: Cuscuta is a plant that takes food from another living plant, so it's a parasite.

Exam Tip: Remember that Cuscuta (Dodder) lacks chlorophyll and obtains nutrients entirely from a host plant, confirming its parasitic nature.

(b) The plant which traps and feeds on insects is:
(i) cuscuta
(ii) china rose
(iii) pitcher plant
(iv) rose
Answer: (iii) pitcher plant
In simple words: A pitcher plant catches and eats insects to get extra nutrients.

Exam Tip: Identify insectivorous plants (like the Pitcher Plant) by their ability to trap insects, which supplements their nutrient intake, especially in nitrogen-poor soils.

Question 9. Match the items given in Column I with those in Column II:

Exam Tip: To score well on matching questions, ensure you understand the specific function or characteristic associated with each term. For instance, chlorophyll's role in leaves, Rhizobium's role in nitrogen fixation, and Cuscuta's parasitic nature are key connections.

Question 10. Mark 'T' if the statement is true and 'F' if it is false:
(i) Carbon dioxide is released during photosynthesis.
(ii) Plants which synthesise their food themselves are called saprotrophs.
(iii) The product of photosynthesis is not a protein.
(iv) Solar energy is converted into chemical energy during photosynthesis.
Answer:
(i) False
(ii) False
(iii) True
(iv) True
In simple words: Plants take in carbon dioxide, they don't release it. Plants that make their own food are autotrophs, not saprotrophs. Photosynthesis makes sugar, not protein. And yes, sunlight energy changes into food energy.

Exam Tip: Review the process of photosynthesis thoroughly: what goes in (CO2, water, sunlight), what comes out (oxygen, glucose/carbohydrate), and the energy conversion (solar to chemical).

Question 11. Choose the correct option from the following: Which part of the plant takes in carbon dioxide from the air for photosynthesis?
(i) Root hair
(ii) Stomata
(iii) Leaf veins
(iv) Petals
Answer: (ii) Stomata
In simple words: Stomata are tiny holes, mostly on leaves, that let the plant breathe in carbon dioxide for making food.

Exam Tip: Remember that stomata are specialized pores, primarily on the underside of leaves, crucial for gas exchange, including the uptake of carbon dioxide for photosynthesis.

Question 12. Choose the correct option from the following: Plants take carbon dioxide from the atmosphere mainly through their:
(i) roots
(ii) stem
(iii) flowers
(iv) leaves
Answer: (iv) Leaves
In simple words: The leaves are the main part of a plant that grabs carbon dioxide from the air because they have tiny holes called stomata.

Exam Tip: Connect the primary function of photosynthesis to the plant's structure; leaves are optimized for capturing sunlight and CO2, making them the main organs for this process.

Question 13. Why do farmers grow many fruits and vegetable crops inside large green houses? What are the advantage to the farmers?
Answer: Cultivating crops within spacious greenhouses offers several benefits. It maintains the necessary temperature for plants and shields them from strong winds, extreme cold, and pests. The main benefits of greenhouse farming include improved crop yield and less labor required from farmers.
In simple words: Farmers use big greenhouses to grow fruits and vegetables because they control the temperature, protect plants from bad weather and insects, which helps them grow more and requires less work.

Exam Tip: When discussing greenhouses, highlight their role in creating controlled environments, protecting crops from adverse conditions, and ultimately leading to better yields with reduced effort.

Extended Learning – Activities And Projects

Question 1. Project: Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in their centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.4). Keep the plant in the sunlight for 2-5 days. Observe the difference in the colour of the covered and Experiment to test the uncovered the occurrence of portions on photosynthesis the leaf. Perform iodine test on this leaf.
Did the two parts show different results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2-3 days and do the iodine test again. Describe your observations.
Answer: The covered part of the leaf shows a pale yellow color, while the exposed portion remains green. After applying iodine solution, only the uncovered area turns blue-black, which confirms the presence of starch.
When the iodine test is done on the second leaf, after allowing the previously covered part to receive sunlight for 2-3 days, the entire leaf shows starch. These findings allow us to conclude that light is essential for photosynthesis to happen.
In simple words: The leaf part covered with black paper turns pale yellow, showing no starch. The uncovered part stays green and turns blue-black with iodine, meaning it has starch. If we then expose the previously covered part to sunlight, it also shows starch, proving sunlight is needed for photosynthesis.

Exam Tip: For experiments on photosynthesis, remember that the absence of light prevents starch formation, which can be detected by the iodine test, highlighting light as a crucial factor.

Question 2. Visit a green house if there is one near your place. Observe how they grow plants. Find out how they regulate the amount of light, water and carbon dioxide to growtheplants.
Answer: A greenhouse is a structure made of glass where plants are kept to shield them from cold weather. These are commonly built in colder areas. The glass panes collect heat from the sun's rays inside the greenhouse, maintaining warmth.
In simple words: Greenhouses are glass houses that keep plants warm by trapping sunlight, mostly used in cold places to protect plants.

Exam Tip: Describe a greenhouse as a controlled environment where factors like temperature, light, and humidity can be managed to optimize plant growth, especially in challenging climates.

Question 3. Try growing a sweet potato just in water. Describe your experiment and observations.
Answer: Get a large beaker or a glass container and fill it three-quarters with water. Place a small sweet potato into the water, ensuring it is fully submerged. After about 4-5 days, you might see the sweet potato beginning to rot. This experiment demonstrates that water alone is insufficient for plant growth.
In simple words: If you put a sweet potato only in water, after a few days, it will start to rot. This shows that plants need more than just water to grow well.

Exam Tip: This experiment illustrates that while water is vital, plants also require nutrients, proper aeration, and often soil for healthy, sustained growth, not just survival.