Download cbse class – x science solutions

CBSE CLASS – X
SCIENCE SOLUTIONS
(CBSE DELHI)
SET – 3
SECTION – B
19.
Name the hormone that helps in regulating level of sugar in our blood. Name the gland that
secrets it.
19.
Hormone : Insulin
Gland : Pancreas
20.
A person lives near a forest. Make a list of four items which he can get from the forest to meet his daily
needs.
20.
Fruits, animal meat, firewood, timber
21.
Name the green dot like structures in some cells observed by a student when a leaf peel was viewed
under a microscope. What is this green colour due to?
21.
Green dot like structures : Chloroplasts Green colour is due to the green pigment chlorophyll.
22.
What is phototropism? Describe an activity to demonstrate phototropism.
22.
The growth movements in plants in response to light as stimulus is said to be phototropism
Activity: To demonstrate phototropism in plants.
Requirements: A potted plant,
Procedure: Take a potted plant and keep it in the sunlight in a horizontal position and observe the
growth of roots and shoots.
Observation: The shoots of the plant grow towards sunlight and roots away from sunlight
Conclusion: Roots are negatively phototropic and shoots are positively phototropic
23.
List any two differences between pollination and fertilisation.
23.
Pollination
1.
2.
24.
Pollination is the process of transfer
of pollen grains from anther to the
stigma of the same or different flower.
It takes place with the help of
pollinations like wind, water insects
etc.
Fertilization
1.
Fertilization is the process of fusion of
male gamete with the female gamete.
2.
It takes place by the growth of pollen
tube towards the ovary.
Give one example each of characters that are inherited and the ones that are acquired in humans.
Mention the difference between the inherited and the acquired characters.
24.
Inherited character : Hair color, eye color
Acquired character : Ear piercing, body weight
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25.
Inherited Characters
Acquired characters
The characters which is passed on
The characters which is acquired by an individual
from the parent to the offspring is
during his life time are said to be acquired
known as inherited character
characters
How is ozone formed in the higher level of atmosphere? “Damage to the ozone layer is a cause of
Concern”. Justify this statement.
25.
The ozone layer is continuously formed in the atmosphere due to the action of UV rays on molecular
oxygen.
The high-energy UV radiations break down O2 molecules present in upper layers of atmosphere into
nascent oxygen.
O 2 ⎯UV
⎯→ O + O
Then, this free oxygen atom combines with an oxygen molecule to form ozone.
O + O2 ⎯
⎯→ O 3 (Ozone)
“Damage to the ozone is a cause of concern”; as ozone depletion has created an ozone hole over the
Arctic region.
Damage in the ozone layer allows the harmful UV rays to enter the Earth. UV rays can cause –
ƒ skin cancer, ageing, and corneal cataracts in human beings.
ƒ death of many phytoplanktons that will lead to increased global warming. Increased global
warming in turn, leads to melting of Arctic ice cap which may result in further increase in the sea
level.
Thus, it is justified to say that damage to the ozone is a cause of concern.
26.
Write the full form of DNA. Name the part of the cell where it is located? Explain its role in the process
of reproduction of the cell.
26.
Deoxyribonucleic acid.
Nucleus of a cell.
It is a chemical, which carries genetic information required by the cells to divide and produce proteins.
During the gamete formation DNA creates its exact copies which are passed to the gamete No
biochemical reaction is 100% accurate; thus leading to variations in the offspring. Also the fusion of
male and female gamete results in the development of variations and thus evolution. Thus it is the DNA
which acts as the blue print and is passed generations over generations.
27.
Explain the process of digestion of food in mouth, stomach and small intestine in human body.
OR
(a)
List the three events that occur during the process of photosynthesis. Explain the role of stomata
in this process.
(b)
27.
Describe an experiment to show that ―sunlight is essential for photosynthesis”.
The process of digestion of food in mouth, stomach and small intestine is described as follows:
Mouth:
Digestion of food begins in the mouth. Saliva present in mouth contains a digestive enzyme called
salivary amylase, which breaks down starch into simple sugar.
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Stomach:
The stomach stores and mixes the food received from the oesophagus with the gastric juices. The main
components of gastric juice are hydrochloric acid, mucus, and pepsinogen.
Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium, pepsinogen is
converted to pepsin, which is a protein-digesting enzyme. Mucus protects the inner lining of the
stomach from the action of HCl. Gastric lipase is also present in the stomach in small amount but it can
not act upon in an acidic medium.
Small intestine:
Small intestine is the site for complete digestion of carbohydrates, proteins, and fats.
The small intestine produces intestinal juice from the glands present in its wall, which helps in further
digestion of food. Small intestine also obtains digestive juices from liver and pancreas that helps in
mixing of food and complete digestion of food.
The liver produces bile juice which causes emulsification of fats and creates basic medium for the
action of the intestinal juices and the pancreas produces pancreatic juice for digesting proteins and
emulsified fats.
This digested food is finally absorbed through the intestinal walls.
OR
(a)
The events that occur in plants during photosynthesis are:
•
Absorption of sunlight by the green pigment chlorophyll.
•
Conversion of light energy into chemical energy and the splitting of water molecule into oxygen
and hydrogen.
•
Reduction of carbon dioxide into glucose.
Role of stomata
Stomata are tiny pores present mainly on the surface of leaves. They are also present on the surface of
young stems and roots. The main function of stomata is the exchange of gases (entry of CO2 and
release of O2) associated with the photosynthesis.
(b)
Sunlight is essential for photosynthesis
Procedure:
1.
Place a healthy green potted plant in a dark room for 1-2 days. This is done to ensure that the
plant consumes all its reserve food and the leaves do not contain any starch.
2.
Then, cover a portion of a leaf of this plant on both sides with two uniform pieces of black paper,
fixed in position with two paper clips.
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3.
Now, expose this plant to bright light. After a few hours, remove the leaf and decolorize it with
alcohol and test the presence of food (starch) with iodine solution.
Observation: It can be observed that the portion of the leaf covered with black paper does not show
any presence of starch (food).
Conclusion: This is because the food prepared by plants through the process of photosynthesis is
stored as starch. Starch reacts with the iodine solution to give blue-black colour.
Only those portions of the leaf that were exposed to sunlight could photosynthesise. Hence, gives blueblack colour when tested with iodine.
The portion of the leaf covered with black paper did not receive sunlight. Hence, starch was not
produced. Thus, it can be concluded that the sunlight is essential for photosynthesis.
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