[2 Mark Questions]

Question 12 Marks

What happens when we are injured and start bleeding?

Answer

In the situation when we are injured we start bleeding.
This bleeding is stopped by clotting mechanism.
Generally, the excessive bleeding would lead to a loss of pressure resulting in reduction of the efficiency of the pumping system.
To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at the point of injury.

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Question 22 Marks

What happens if blood vessels develops a leak?

Answer

In the situation when we are injured we start bleeding.
This bleeding is stopped by clotting mechanism.
Generally, the excessive bleeding would lead to a loss of pressure resulting in reduction of the efficiency of the pumping system.
To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at the point of injury.

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Question 32 Marks

Why do in plants sometimes $CO_2$ eliminate and sometimes $O_2$ in air?

Answer

Plants exchange gases through stomata and the large intercellular spaces of cells that are in contact with air.
Carbon dioxide and oxygen are exchanged by diffusion.
Carbon dioxide and oxygen can go into cells or away from them and diffuse out into the air.
The direction of diffusion depends upon the environmental conditions and the requirements of the plant.
At night, when there is no photosynthesis elimination of $CO_2$ is major exchange activity taking place.
During the day $CO_2$ produced during respiration is used up for photosynthesis, hence there is no $CO_2$ release.
Instead, oxygen release is the major event during day.

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Question 42 Marks

Explain gaseous exchange in plants.

Answer

Plants exchange gases through stomata and the large intercellular spaces of cells that are in contact with air.
Carbon dioxide and oxygen are exchanged by diffusion.
Carbon dioxide and oxygen can go into cells or away from them and diffuse out into the air.
The direction of diffusion depends upon the environmental conditions and the requirements of the plant.
At night, when there is no photosynthesis elimination of $CO_2$ is major exchange activity taking place.
During the day $CO_2$ produced during respiration is used up for photosynthesis, hence there is no $CO_2$ release.
Instead, oxygen release is the major event during day.

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Question 52 Marks

What are the functions of the acid in our stomach?

Answer

Role or Functions of the acid:
$(1)$ Acid destroys the bacteria and other microorganisms that enter the stomach, along with the food.
$(2)$ It converts the inactive enzyme pepsinogen into active enzyme pepsin.
$(3)$ It provides acidic medium required for the action of pepsin.
Pepsin can digest proteins present in food only in acidic medium.
$(4)$ Insoluble mineral salts get dissolved in acid.

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Question 62 Marks

What is the role of the acid in our stomach?

Answer

Role or Functions of the acid:
$(1)$ Acid destroys the bacteria and other microorganisms that enter the stomach, along with the food.
$(2)$ It converts the inactive enzyme pepsinogen into active enzyme pepsin.
$(3)$ It provides acidic medium required for the action of pepsin.
Pepsin can digest proteins present in food only in acidic medium.
$(4)$ Insoluble mineral salts get dissolved in acid.

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Question 72 Marks

Explain the types of organisms on the basis the modes of nutrition.

Answer

The requirement for energy and materials is common in all organisms.
On the basis of the mode of nutrition, organisms are of two types:
$(1)$ Autotrophs:
These organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water.
Green plants and some bacteria are autotrophs.
$(2)$ Heterotrophs:
These organisms utilise complex substances from other organisms and broken down into simpler ones.
To achieve this, organisms use bio-catalysts called enzymes.
The heterotrophs survival depends directly or indirectly on autotrophs.
Animals and fungi are heterotrophs.

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Question 82 Marks

How do living things get their food?

Answer

The requirement for energy and materials is common in all organisms.
On the basis of the mode of nutrition, organisms are of two types:
$(1)$ Autotrophs:
These organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water.
Green plants and some bacteria are autotrophs.
$(2)$ Heterotrophs:
These organisms utilise complex substances from other organisms and broken down into simpler ones.
To achieve this, organisms use bio-catalysts called enzymes.
The heterotrophs survival depends directly or indirectly on autotrophs.
Animals and fungi are heterotrophs.

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Question 92 Marks

Give scientific reason : The parasitic mode of nutrition is harmful for the host organism.

Answer

In parasitic nutrition, one organism depends fully for obtaining its nutritional needs, directly on other living organism.
The latter is called a host from whom the parasite directly obtains food.
The parasitic organism keeps close contact with the host and sucks or absorbs nutrients from its body.
The host goes on becoming weaker physically and physiological.
The health of host thus is affected.
Thus, the parasitic mode of nutrition is harmful for the host organism.

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Question 102 Marks

Write short note: $ATP$

Answer

$ATP$ (Adenosine TriPhosphate) is the energy currency for cellular processes.
Synthesis of $ATP:$
The energy released during cellular respiration is immediately used to synthesise $ATP$ molecule from $ADP$ and inorganic phosphate $[( P )]$..
$ADP +( P \xrightarrow{\text { Energy }} ADP \sim p = ATP$
Stored energy:
The terminal phosphate linkage in $ATP$ is broken down using water, the energy equivalent to $30.5 \ k J/ mol$ is released.
That means this much energy is stored in terminal phosphate linkage.
Use of $ATP:$
Endothermic processes in the cell use $ATP$ to drive the reaction.
$ATP$ can be used in the cells for the contraction of muscles, protein synthesis, conduction of nerve impulse and many other activities.

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Question 112 Marks

Where do plants get each of the raw materials required for photosynthesis?

Answer

Raw materials required for photosynthesis:
$(1)$ $CO_2$: Plants get it from atmosphere.
$(2)$ $H_2O$: Plants root absorbed it from soil.
$(3)$ Energy: Plants get it directly from sun.

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Question 122 Marks

How do desert plants differ from other plants grown in normal habitat on the basis of reduction of $CO_2?$

Answer

Plants grown in normal habitat take up carbon dioxide during day and synthesise carbohydrates during day time.
Whereas desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by chlorophyll during the day.

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Question 132 Marks

Write short note on autotrophic nutrition.

Answer

Autotrophic nutrition is shown by all photosynthetic organisms.
Photosynthesis is a process in which carbon dioxide and water are converted into carbohydrates in the presence of sunlight and chlorophyll.
All the green plants show autotrophic nutrition, by which they produce starch and some proteins.
Carbohydrates are utilised for providing energy to the plants.
The excess carbohydrates are stored in form of starch, which is a complex carbohydrate.
It serves as the internal reserve energy to be used as and when required.

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Question 142 Marks

Why the energy and the materials from outside are needed in our body? What is the source for these?

Answer

When we walk or ride a bicycle or do any apparent activity, we are using up energy.
Even when we are not doing any apparent activity, energy is needed to maintain a state of order in our body.
We also need materials from outside in order to grow, develop, synthesise protein and other substances needed in the body.
The food we eat is the source of energy and materials.

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Question 152 Marks

What are outside raw materials used for by an organisms?

Answer

Name of outside raw materials	Used for
$1.$ $CO_2$	Photosynthesis by plants
$2.$ Carbon based food source	Respiration by aerobic organisms

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Question 162 Marks

Why is diffusion insufficient to meet the oxygen requirement of multicellular organisms like humans?

Answer

In multicellular organisms like human, all the cells are not in direct contact with the surrounding environment.
The body structure is more complex and the body size is also large.
Therefore, simple diffusion will not be sufficient to send oxygen to every cell.
It has been estimated that a period of $3$ years would be needed to carry a molecule of $O_2$ from our lungs to reach our toes through diffusion.
So, diffusion is insufficient to meet the oxygen requirement of multicellular organisms like humans.

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Question 172 Marks

Why are molecular movements needed for life?

Answer

Living organisms are made up of cells and tissues.
Due to natural wear and tear, the orderliness of structure of body may be lost.
Therefore, molecular movements are needed for repair and maintenance of the body.
This keeps the body alive.

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Question 182 Marks

How is the amount of urine produced regulated?

Answer

The amount of urine formed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted.
More water and dissolved wastes in the body will produce more urine.
On the other hand, less water and less dissolved wastes will produced less urine.

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Question 192 Marks

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Answer

It is necessary to separate oxygenated and deoxygenated blood in mammals and birds because it allows a highly efficient supply of oxygen to the body and this is useful in their high energy needs for to maintain constant body temperature.

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Question 202 Marks

Give scientific reason : Respiration is important to keep the organism in living state.

Answer

The living cells of the body need energy for performing various vital functions.
The energy is obtained by the biological oxidation of organic nutrients in the cell.
The process of breakdowm of food sources for cellular needs either using oxygen or without called is respiration.
The energy, so released is for continuation of various functions and thereby maintaining the living state of the organism.
Thus, respiration is essential for life.

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Question 212 Marks

Give scientific reason : Bile is an important digestive juice though it does not contain any digestive enzymes.

Answer

Bile is a greenish yellow alkaline digestive juice secreted from the liver cells.
Bile contains bile salts, certain bile pigments but does not contain any digestive enzymes.
The bile salts turn the acidic food from stomach, alkaline and thereby provide alkaline medium for further reactions in intestine.
Pancreatic enzymes and intestinal enzymes need alkaline medium.
Bile salts emulsify the large fat globules into a very large number of very minute fat droplets and thereby greatly increase the exposed surface area of fat for the rapid action of lipases.
Hence bile is an important digestive juice though it does not contain any digestive enzymes.

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Question 222 Marks

Give scientific reason : The length of small intestine of herbivorous is relatively much longer than that of carnivorous.

Answer

The length of small intestine is different in different animals and that depends upon the nature of food taken by the animal.
The carnivorous eat flesh.
The digestion of flesh as food is quite easy and rapid and there is very small amount of roughage.
Hence these animals have short small intestine.
The herbivorous eat grass and other vegetation.
The cellulose of the plant cells is a complex substance and its complete digestion needs more space and time
and hence longer small intestine and longer large intestine.
Hence, the length of small intestine of herbivorous is relatively much longer than that of carnivorous.

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Question 232 Marks

Give scientific reason : $HCl$ (Hydrochloric acid) is an important constituent of gastric juice.

Answer

For the chemical digestion of food in stomach, the stomach secretes gastric juice from its gastric glands.
$HCl$ is one of the constituents of gastric juice.
$HCl$ destroys the bacteria and other microorganisms entering along with the ingested food and thereby prevent the decay of food in stomach.
$HCI$ provides acidic medium for the action of gastric enzyme.
$HCI$ converts inactive enzyme pepsinogen into an active enzyme pepsin.
Pepsin acts in acidic medium on proteins and starts their digestion and convert them into preoteoses and peptones. Thus, $HCI$ is an important constituent of gastric juice.

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Question 242 Marks

Give scientific reason : The stomata in leaves keep on opening and closing

Answer

On one or both the surfaces of the leaves of flowering plants, there are numerous stomata as minute pores.
Each of these pores is guarded by a pair of guard cells.
The opening and closing of the stomata is controlled by these guard cells, which contain chloroplasts.
When water enters the guard cells, the latter swell and cause the opening of stomata and when the guard cells lose water, the guard cells contract and cause the closing of stomata.
Thus, the stomata in leaves keep on opening and closing due to entry and exit of water in the guard cells.

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Question 252 Marks

Give scientific reason : The organisms possessing chlorophyll are autotrophs.

Answer

The organisms, possessing chlorophyll, can trap and utilize the solar energy to synthesize their own food using $CO_2$ and water.
This process of trapping the solar energy for synthesis of ones own food is called photosynthesis and the mode of nutrition of such organisms is called autotrophic.
In photosynthesis, the food synthesized is the simplest hexose sugar-glucose, which is utilized for obtaining energy.
The surplus glucose is stored as reserve food in the form of starch.
Hence, the organisms possessing chlorophyll are autotrophs.

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Question 262 Marks

Give scientific reason : The wall of the artery is thick and elastic while that of vein is relatively thin.

Answer

The arteries carry blood from the heart towards different organs.
When the ventricles contract, the blood is pushed in the arteries under high pressure.
In order to withstand this pressure, the arteries must have thick and elastic walls.
The veins receive blood from different organs and carry it to the heart.
The blood in the veins flows at relatively low pressure.
Hence, the wall of the veins is relatively thin and less elastic.

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Question 272 Marks

Give scientific reason : Lymph separates from the blood and remixes with the blood.

Answer

The lymph oozes out through the pores in thin walls of the blood capillaries, as a fluid from the blood flowing through the capillaries.
It flows very slowly in the intercellular spaces between the tissue cells.
The intercellular spaces have no walls of their own and are called lymph capillaries.
These lymph capillaries meet and join with each other to form larger ones which finally open in a vein to pour its contents.
Thus, lymph, as a colourless watery fluid collects in a large lymph vessels that finally open in particular veins in the body to pour its contents back in blood.

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Question 282 Marks

Give scientific reason : The right side chambers of the heart have deoxygenated blood and left side chambers have oxygenated blood in them.

Answer

The four-chambered heart, in man, is formed of two atria and two ventricles.
All the four chambers of the heart are separated from each other by septa.
Deoxygenated blood from different organs of the body (except lungs) is brought through superior and inferior vena cava and poured in the right atrium and then into the right ventricle.
Similarly oxygenated blood from the two lungs is brought through pulmonary veins and poured in the left atrium and then into the left ventricle.
The four-chambered heart prevents the mixing of oxygenated blood with deoxygenated blood.
Hence, the right side chambers of the heart have deoxygenated blood and the left side chambers have oxygenated blood in them.

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Question 292 Marks

Give scientific reason : Translocation in the phloem takes place in both upward and downward direction.

Answer

The phloem transports amino acids, various plant hormones substances in addition to the products of photosynthesis.
Carbohydrates are synthesized in the leaves due to photosynthesis.
These carbohydrates are transported to the roots and stem through phloem.
The plant hormones synthesized in shoot apex flow downwards through the phloem and the plant hormones synthesized in the root apex and the food reserve stored in roots are transported upwards through the phloem.
Thus, the translocation in the phloem takes place in both, upward and downward directions.

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Question 302 Marks

Give scientific reason : In very tall plants, the suction force created due to transpiration is the main conducting force for water and mineral ions through the xylem.

Answer

The xylem tissue in all the organs of a plant remains connected to each other and forms a continuous path for the flow of water, etc.
Thus, a continuous water column is formed therein.
Mere root pressure, created in small herbs, is not sufficient to push water and minerals to the great height of very tall plants.
The plants adopt another way to reach the target of fulfilling the water requirement.
Evaporation of water molecules in the form of vapour occurs through stomata.
Due to that a suction force arises in the cells of leaves.
This of suction force comes into being from the cells of the leaves and is gradually experienced in the xylem of roots.
As a result, in very tall plants, the suction force created due to transpiration is the main conducting force for water and mineral ions through the xylem.

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Question 312 Marks

Give scientific reason : Proper transportation (conducting) system is necessary in higher plants.

Answer

The green leaves of plants obtain $CO_2$ from the atmosphere and synthesize carbohydrates.
The plants, through their roots, absorb water and other raw mineral elements essential for the constitution of the body, from the soil.
In higher plants the distance between the roots and the leaves being more, the water, mineral elements and the products of photosynthesis cannot be sent to all the different parts of the plant body, merely by diffusion from cell to cell.
Therefore, in order to distribute all these substances rapidly and timely, a proper transportation (conducting) system is necessary in higher plants.

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Question 322 Marks

Describe double circulation of blood in human beings. Why is it necessary?

Answer

Blood passes through the heart twice during each cycle in human beings.
This is called double circulation.
[Deoxygenated blood from different organs is drained and finally through vena cava it is poured in right atrium. From here this blood is transported to lungs via right ventricle. In lungs, blood become oxygenated and is again transported to left atrium. From here it transports in left ventricle and then by aorta to different body parts.]
It is necessary because it allows a highly efficient supply of oxygen to the body cells, which fulfill the high energy need of body.

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Question 332 Marks

What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer

A deficiency of haemoglobin in our bodies leads to a disease called anaemia.
Due to this, cells of our body do not get sufficient oxygen for cellular respiration, which may lead to release less energy.
Weakness, fatigue, tiredness, etc. conditions may arise.

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Question 342 Marks

How are the alveoli designed to maximize the exchange of gases?

Answer

The alveoli are located at the terminal ends of bronchioles. They are balloon-like structures provides large surface area for exchange of gases with an extensive network of blood vessels.

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Question 352 Marks

Explain: Why using visible movement as the defining characteristic of life is not enough.

Answer

Running, chewing, shouting, etc. are common examples of voluntary movements.
Even animals / human when asleep, show breathing which is one kind of involuntary movement.
The growth of plant is considered as a movement.
Involuntary movements in animals and growth related movements in plants may not be visible.
But still they indicate life.
Molecular movements are also invisible, which still keep the bodies alive.
So, using visible movement as the defining characteristic of life is not enough.

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Question 362 Marks

How is oxygen and carbon dioxide transported in human beings?

Answer

In human beings, the respiratory pigment haemoglobin has high affinity for Oxygen, so it is mostly transported by haemoglobin.
Carbon dioxide is more soluble in water than Oxygen and hence it is mostly transported in dissolved form in our blood.

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Question 372 Marks

What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Answer

The amount of dissolved oxygen is fairly low in aquatic environment as compared to the amount of oxygen in the air.
So, terrestrial organisms fulfil their oxygen demand with low breathing rate as compared to aquatic organisms.

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Question 382 Marks

Why respiratory pigment is essential in human beings?

Answer

When the body size of animals is large, the diffusion pressure alone cannot be sufficient to deliver oxygen to all parts of the body in short time.
If diffusion were to move oxygen in our body, it is estimated that it would take $3$ years for a molecule of oxygen to get to our toes from our lungs.
Instead, respiratory pigment haemoglobin present in the red blood corpuscles, take up oxygen from the air in the lungs and carry it to tissues and cells of body through blood circulation.
Oxygen is released to oxygen deficient tissue.
Haemoglobin has a high affinity for oxygen, so it carries oxygen to all the cells of the body.
So, respiratory pigment is essential in human beings.

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