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1. D. Answer the following questions in brief:
1. A: The (main) factors that determine the shape of a cell are location and function.
2. A: Distinguish between unicellular and multi cellular organisms are:
Unicellular organisms are made up of a single cell. e.g., Euglena and Amoeba.
Multicellular organisms are made up of many cells. e.g., Humans and Birds.
3. (a) A: All organisms are made up of cells. A cell is capable of independent existence. Due to this, cell is called the
structural and functional unit of life.
(b) A: Cell wall is present in plant cell. Due to this, plant cells are more rigid than animal cells.
4. A: Mitochondria is known as the Powerhouse of the cell.
Mitochondria are the site of cellular respiration. Energy is produced during this process. Due to this, mitochondria
are called the Powerhouse of the cell.
5. A: Chloroplast is responsible for imparting colour to the leaves. Chromoplast is responsible for imparting colour
to fruits.
6. A: Cilia and flagella are extensions on the cell membrane, these help in locomotion and procurement of food in
organisms like Amoeba and Paramoecium. Cilia are much smaller than flagella.
7. A: In Onion peel cells:
 Cells are arranged in rows.
 Cell wall is present.
In Cheek cells:
 Cells randomly arranged.
 Cell wall is absent.
E. Answer the following questions.
1. A: three different cell types found in human beings are:
These figures clearly show that liver cell is irregular in shape, fat cell is spherical and muscle cell is spindle-
shaped. This shows that all cells in an organism do not have the same shape.
2. A: Chromosomes are formed in the nucleus during cell division. When the cell is ready to divide, the chromatin (in
nucleus) condenses to form thicker, thread-like chromosomes. Chromosomes are responsible for inheritance of
characters from one generation to the next generation.
4. (a) Endoplasmic Reticulum- It is a network of membranes. It provides channels for transport of materials in a
cell.

2. (b) Golgi Complex- They are sac-like structures stacked one above the other. They are involved in the processing
and packaging of materials produced by the cell.
(c) Nucleus- a specialised structure in the cells, bound by the nuclear membrane; responsible for controlling all
cellular activities.
(d) Chromo plasts- They are responsible for imparting colour (other than green) to the different parts of the plant.
(e) Vacuoles- It appears as an empty space in the cytoplasm. It is generally large in plant cells. It stores excess of
water and waste products.
(f) Mitochondria- These are rod-shaped or spherical structures. They are responsible for cellular respiration and
for generation of energy for different activities of life.
5. A: When the cell membrane gets damaged, it exposes the cell’s contents to external environment. This results in
stoppage of all functions of the cell, and eventually to cell death.
6. A: The cell is the basic structural, functional, and biological unit of all known organisms. A cell is the smallest
unit of life, and therefore, cells are often described as the “building blocks of life”.
The different organelles that make a cell are nucleus, Golgi complex, mitochondria, chloroplast, endoplasmic
reticulum, vacuole and ribosome.
All these cell organelles work together to perform different functions of the cell. None of these is capable of
independent existence. So, they are not called the structural and functional unit of life.

3. D. Answer the following questions in brief.
1. A: A virus behaves like a non-living when it is outside a host cell. Once a virus enters a host cell, it starts to
behave like a living being. Due to this, viruses are considered as the borderline between living and non-living.
2. A: An anaerobic process through which sugars/carbohydrates are converted into alcohol or acids and carbon
dioxide by microorganisms is called fermentation.
Fermentation is useful in the food and beverages industries in various ways:
 It helps in making tasty dosa.
 It helps in making bread and cake.
 It helps in making wine
3. A: When a plant or animal dies, its remains are decomposed by microorganisms. Decomposition is the process
through which all constituent materials of a living being are sent back to the environment. Had there been no
microorganisms, dead remains of plants and animals would be keeping on accumulating all around us. So, it can be
said that in the absence of microorganisms the earth would become a heap of dead plants and animals.
4. (i) A: Nitrogen
(ii) A: Pea plants give shelter to Rhizobium bacteria. These bacteria carry out nitrogen fixation in soil. Thus, pea
plants help in replenishing nitrogen in soil.
5. A: Microorganisms reproduce at a faster rate between 20 to 40°C. They reproduce at a much slower rate when
temperature is below this range. Milk is converted into curd by multiplication of lactobacillus. This is why it takes
less time to prepare curd in summers as compared to preparing it in winters.
6. A: (a) By female Anopheles mosquito.
A: (b) Through cough droplets in air.
A: (c) Through cut by a rusted iron article.
A: (d) Through contaminated food and water.
7. A: Antibiotics are chemicals that inhibit the growth of (other) harmful microorganisms by affecting their life
processes. Antibiotics are prepared from microorganisms. Two examples are Penicillin and Streptomycin.
E. Answer the following questions.
1. A: Microorganisms are very useful in manufacturing different food items in various ways. They are used in
making tasty dosa. It helps in making bread and cake. Many microorganisms are used in the manufacture of
alcohol, wine and acetic acid.
2. (a) A: Yeast is added to the batter so that fermentation take place. It causes it to increase in volume and makes it
fluffy and soft.
(b) A: It is important to brush one’s teeth before going to bed because bacteria can grow on food particles that get
lodged in between our teeth. Acid produced by these bacteria, corrode the tooth enamel and cause cavities. Hence
it is important to brush one’s teeth before going to bed.

4. (c) A: Salt reduce the water content of pickle and make it unavailable for the growth of microorganisms. As the
result pickle gets preserved. If the quantity of salt is reduced then it increases the growth of microorganisms and
can it to go bad soon.
(d) A: Enlarged or puffed can represent that there had been some bacterial action on the item which might lead to
formation of toxic substance.
(e) A: One should take out only required quantity of frozen food as it might spoil the rest of food item and refrozing
the frozen item destroys its nutrients.
3. A: Communicable diseases spread from one person to another through air, water, food, physical contact or
insects.
(a) Tuberculosis- It can be prevented by vaccination.
(b) Athlete’s foot- It can be prevented by maintaining good personal hygiene.
(c) Cholera- Cholera can be prevented by proper disposal of waste and using disinfected water.
4. A: Some microorganisms cause diseases in human beings, plant and animals. Such diseases causing organisms
are known as pathogens.
Bacteria and Fungi are the examples of pathogens which cause diseases in plants and animals.
5. A: This could happen due to consumption of contaminated food. This disease is called food poisoning. Food must
be properly prepared and stored to prevent food poisoning.
6. (a) A: Cholera
(b) A: Ringworm
(c) A: Rabies
(d) A: Malaria
(e) A: Common cold.

5. D. Answer the following questions in brief.
1. A: Vibration.
2. A: Guitar and Sitar.
3. (a) A: Gas.
(b) A: Solid.
4. (a) amplitude
A: The maximum displacement of a vibrating body on either side of its central/mean position is called amplitude. Its
SI unit is metre.
(b) time period
A: The time taken by a vibrating body to complete one vibration. (or time taken for one complete cycle of vibration
about a given mean point.) The SI unit of time period is second.
(c) frequency
A: the number of cycles of vibrations in one second is called frequency. The SI unit of frequency is hertz (Hz).
5. A: (a) Amplitude is the characteristic of a vibrating body which determines the loudness produced by it.
A: (b) Frequency is the characteristic of a vibrating body which determines the pitch of the sound produced by it.
6. A: Male.
(b) A: Female.
7. A: A given sound regarded as a ‘musical sound’ or ‘music if it is produced by regular, or periodic vibrations and
make us feel comfortable.
E. Answer the following questions.
1. A: It is the voice box, or the larynx, of the human body system that helps us to produce sound. The voice box has
two vocal chords stretched across it. They are stretched across the voice box in such a way that there is a narrow
gap, or slit between them. Air can pass through this slit. The lungs force air through the slit between the vocal
chords and this make them vibrate and produce sound.
2. A: The mechanism of production of sounds in birds differ from that in human beings. Birds have a ring of
cartilage, called syrinx, in their wind pipe. They use it in their voice box to produce their characteristics sounds.
While in human beings have voice box (larynx) to produce sound.
5. A: The speed of light is more than the speed of sound. Due to this, we always hear the thunder a little after we see
the flash of lightning.
Explanation:

6. Measurements, of the speed of light and sound, tell us that light propagates very fast as compared to sound. The
speed of sound in air is nearly 330 ms-¹ (or 0.33 km per second) and the speed of light (in vacuum) is as high as
(nearly) 3 lakh kilometres per second. Light, thus, propagates nearly a million times faster than the sound. Hence,
when lighting and thunder occur together, the flash of lighting reaches us in practically zero time. The sound of the
thunder, however, takes a few seconds to reach us. We, therefore, hear the thunder a little later after seeing the
flash of light.
6. (a) A: Loudness: the ‘sensation, produced in the human ear, which helps to distinguish between the impact of
different sounds on the drum of the human ear.
Pitch: a characteristic of sound which helps in differentiating a shrill sound from a flat sound.
(b) (i) A: The loudness of a sound increases when the amplitude of the vibrating body increases.
(ii) A: The pitch of a sound increases when the frequency of the vibrating body increases.
7. A: Noise pollution is regarded as harmful for humanbeings due to the following reasons:
The most immediate effect is deterioration of mental health. Continuous noise can create panic. The affected
person may become jumpy and her/his frustration level may increase. It may also result in lack of concentration of
mind.
Noise pollution also effects human heart. It may also cause: lack of sleep, hypertension, nervousness, anxiety,
decrease in ability to memorise and extreme emotional behaviour.
Noise pollution may lead to hearing impairment. On short term basis, noise pollution can cause temporary
deafness. If the noise pollution continues over a long period of time, the person may get permanent damage in
her/his ears.