Madhyamik Class 10 Life Science Solved Paper 2020

Medulla Oblongata-Control of heartbeat and swallowing of food

Helps in the conversion of fat and protein into glucose

A-(iii) B-(i) C-(ii)

(b) (A) Anaphase (B) Prophase

(d) More wastage of pollen grains

(b) 1

(a) BbRr, BBRr

(b) Length of stem – dwarf, form of ripe seed – wrinkled

(d) H||h,  H|↑

(b) Interspecific struggle

(c) Glycine, Alanine

(b) Inform other worker bees about the direction and the distance of the source of food from the bee hive

(a) Conservation is promoted to local people and other biotic communities along with the conservation of the ecosystem

(d) Greenhouse gas – Eutrophication

(c) Sunderbans

1. Sensitivity
2. 88
3. Haemophilia / Colour blindness
4. 3rd
5. Nitrification
6. Ground/ Fresh/ Drinking

1. True
2. False. Crossing over is the exchange of genetic material between homologous chromosomes. It takes place during meiosis, not mitosis.
3. False. Mendel did not use the term gene. He called the units of heredity “factors”. The term gene was coined by Wilhelm Johannsen in 1909.
4. True
5.  True
6. False

1 – (d), 2 – (g), 3 – (a), 4 – (e), 5 – (b), 6 – (c)

1. The odd one is Pons. The other three are parts of the forebrain, while the pons is part of the hindbrain.
2. Schwann cells are located in the peripheral nervous system.
3. Spore
4. The law of independent assortment. This law states that the alleles of different genes assort independently of each other during meiosis.
5. The ABO blood group is an example of a variation that is found among healthy persons and is transmitted through generations.
6. Chimpanzees use stones to break open the hard shells of nuts. They will often carry a stone around with them and use it to crack open the nuts as they find them.
7. The term that includes the other three is Air Pollution.
8. The practice is called Joint Forest Management (JFM)

	Hormone	Nervous System
Nature of function	Chemical	Physical
Pace of Function	Slow	Fast
Time soan of function	Long	Short
Fate	Inactive	Unchanged

• Cause – Flattened of eye ball.
• Remedy – To use spectacle with a convex lens

Synthetic plant hormones can be a valuable tool for increasing crop yields and solving the problem of weeds in agriculture. However, it is important to use them carefully and responsibly, as they can also have negative environmental impacts.

Partially valid. While LH (Luteinizing Hormone) and ICSH (Interstitial Cell-Stimulating Hormone) do play a role in controlling certain reproductive hormones, they do not solely control the secretion of all hormones in the reproductive glands.

the key differences between mitosis in plant cells and animal cells, based on the formation of spindle fibres and the process of cytokinesis:Spindle fibres

• Plant cells: Plant cells do not have centrioles, so the spindle fibres form from the centrosomes, which are small, dense structures located in the cytoplasm.
• Animal cells: Animal cells have centrioles, which are located near the nucleus. The spindle fibres form from the centrioles and extend towards the opposite poles of the cell.

Cytokinesis

• Plant cells: In plant cells, cytokinesis occurs by the formation of a cell plate, which is a new cell wall that grows in between the two daughter cells.
• Animal cells: In animal cells, cytokinesis occurs by the formation of a cleavage furrow, which is a groove that forms in the middle of the cell and eventually pinches the cell in two.

Due to loss of control of the cell cycle, the cell division takes place uncontrolled due to which numerous daughter cells are formed causing the formation of tumours. Such tumours cause cancer later on.

One example of a plant that utilizes adventitious leaf buds for natural vegetative propagation is the Bryophyllum plant. Bryophyllum produces adventitious buds along the margins of its leaves. When these leaves fall on the ground and come in contact with suitable conditions, such as moist soil, these adventitious buds develop into new plants with roots and shoots.

The father is more important than the mother in determining the sex of their offspring. This is because the sex of a child is determined by the sex chromosomes that are passed on from the parents. In humans, the sex chromosomes are X and Y. Females have two X chromosomes, while males have one X chromosome and one Y chromosome.

Round Yellow :	Round Green	Wringked Yellow
RRYY RRYy RrYY RrYy	RRyy Rryy	rrYY rrYy

Here are some suggestions that can be given to a pair of contenders before marriage in order to prevent the spread of a genetic disease from society:

• Genetic counselling: This is a process where a couple can meet with a genetic counsellor to discuss their family history and the risk of passing on a genetic disease to their children. The counsellor can help the couple to understand the risks and options available to them.
• Premarital genetic testing: This is a test that can be used to determine if a couple is a carrier of a genetic disease. If both partners are carriers, there is a risk that their child could be born with the disease.
• In vitro fertilization: This is a procedure where eggs are fertilized in a laboratory and then implanted in the woman’s uterus. This can be used to select embryos that are not carriers of a genetic disease.

Struggle for existence – Tilapia fishes have to face a struggle for existence for food and shelter among the fishes. The competition for food among different fishes in the pond will start. They have to face a struggle against the adverse physical and other conditions of the pond.

The roles air sacs of pigeons play to fly in the air are:-

1. Airsacs reduce the specific gravity of the bird in the air.
2. They naturally reduce friction during flight.
3. They are helpful in reducing the body temperature.
4. Help in dual respiration.

The two features that mentioned, structure and function, are important in defining analogous organs. The structure of an organ is its physical appearance, while the function of an organ is what it does. Analogous organs have similar functions, but they have different structures. This is because they evolved independently from each other.

Here are some ways in which global warming and acidification of soil and water can disturb the nitrogen cycle:Global warming:

• Increased temperatures can lead to changes in the rate of decomposition of organic matter, which can release more nitrogen into the atmosphere.
• Higher temperatures can also lead to changes in precipitation patterns, which can affect the amount of nitrogen that is deposited in soils and water bodies.

Acidification of soil and water:

• Acidification can make it difficult for plants to take up nitrogen, which can lead to a decrease in the amount of nitrogen available in the ecosystem.
• Acidification can also damage the soil and water, making it more difficult for bacteria and other organisms to decompose organic matter and release nitrogen.

Here are some of the causes of the endangeredness of Hilsa, bees, penguins, and Rauwolfia:Hilsa:

1. Overfishing
2. Habitat loss due to coastal development
3. Pollution

Bees:

1. Colony collapse disorder
2. Habitat loss due to agricultural intensification
3. Pesticide use

Penguins:

1. Climate change
2. Overfishing
3. Oil spills

Rauwolfia:

1. Overharvesting
2. Habitat loss due to deforestation
3. Competition from other medicinal plants

People’s Biodiversity Register (PBR) :

1. PBR promotes conservation.
2. It motivates common people to create awareness about the management of natural resources.

1. Cutting of Trees.
2. Killing of animals.
3. Fishing
4. Blowing of Motor horns

Feature	Mitosis	Meiosis
Site of occurrence	All cells of the body	Germ cells only
Nature of division of chromosomes	Equational division	Reductional division
Number of cells produced	2 daughter cells	4 daughter cells
Crossing over	No	Yes

Here are some of the changes in sense organs and bones that occur during the senescence phase of human development:

Sense organs:

• Vision: The lens of the eye becomes less elastic, which can lead to presbyopia, or difficulty seeing close objects.
• Hearing: The hair cells in the inner ear become damaged, which can lead to hearing loss.

Bones:

• Bone mass: Bone mass decreases, which can lead to osteoporosis, a condition in which bones become weak and brittle.
• Joints: The cartilage in joints wears down, which can lead to pain and stiffness.

Here is the importance of the following parts of a eukaryotic chromosome:(a) Centromere

• The centromere is a specialized region of a chromosome that is responsible for the attachment of spindle fibres during cell division.
• It is also important for the segregation of chromosomes during cell division, ensuring that each daughter cell receives the correct number of chromosomes.

(b) Telomere

• Telomeres are the caps at the ends of chromosomes that protect them from degradation.
• They also play a role in the regulation of cell division, as they shorten with each cell division.

Here is the role of cell divisions in controlling growth, reproduction and repair in an organism:

• Growth: Cell division is essential for the growth of an organism. As cells divide, they increase in size and number, which allows the organism to grow larger.
• Reproduction: Cell division is also essential for reproduction. Germ cells, such as sperm and eggs, are produced by cell division. These cells then fuse together to form a new organism.
• Repair: Cell division can also help to repair damaged cells. When a cell is damaged, it can divide to produce new cells that are not damaged. This can help to prevent the spread of damage and to restore the function of the organism.

Here are three pairs of dominant-recessive traits of pea plants as selected by Mendel:

Trait	Dominant allele	Recessive allele
Flower colour	Purple	White
Seed shape	Round	Wrinkled
Seed colour	Yellow	Green

Mendel’s law of dominance states that when two alleles for a trait are different, the dominant allele will be expressed and the recessive allele will be masked. This means that if an individual inherits one dominant allele and one recessive allele for a trait, they will express the dominant trait.

Sex chromosome of Father – XY (Normal Male)Sex chromosome of Mother – X°X (Colour Blind Female)

Male →	Xo	Y
Female ↓
Xo	XoX	XoY
X	XoX	XY

50% of daughters will be colour-blind.

50% of daughters will be carriers of colour blindness.

The first law of Mendel, also known as the law of segregation, states that when two alleles for a trait are present in an individual, only one of the alleles will be expressed in the phenotype. The other allele will be hidden, or recessive.

	R	r
R	RR	Rr
r	Rr	rr

The Four-O’clock plant is a good example of a deviation from the first law of Mendel. In this plant, the colour of the flower is determined by two alleles: R for red and r for white. When a plant that is homozygous for red (RR) is crossed with a plant that is homozygous for white (rr), all of the offspring in the F1 generation will be red. This is because the R allele is dominant over the r allele.

• Prodigality of production: According to Darwin’s evolutionary theory, organisms tend to produce more offspring than can survive to adulthood. This excess production leads to competition for limited resources, as not all individuals can survive and reproduce successfully.
• Origin of variation: Darwin proposed that variation exists among individuals within a population. This variation arises through mechanisms such as genetic mutations and genetic recombination during sexual reproduction. It is the raw material upon which natural selection acts.
• Natural selection: Natural selection is the process by which certain heritable traits become more or less common in a population over time. Individuals with advantageous traits that increase their chances of survival and reproduction are more likely to pass on those traits to the next generation. This results in the gradual accumulation of beneficial traits in a population, leading to adaptation and evolution.

(a) Non-biodegradable insecticides

• Environment: Non-biodegradable insecticides can persist in the environment for long periods of time, and they can accumulate in the food chain. This can have a negative impact on wildlife, as well as on humans who consume contaminated food.
• Human health: Non-biodegradable insecticides can cause a variety of health problems, including cancer, reproductive problems, and neurological damage.

(b) Pollen grain

• Environment: Pollen grain can be a nuisance, and it can also cause allergies in some people.
• Human health: Pollen grain can trigger allergic reactions in some people, which can cause symptoms such as sneezing, coughing, and wheezing. In severe cases, allergies can lead to anaphylactic shock, which can be fatal.

(c) Chemical fertilizers containing phosphate and nitrate

• Environment: Chemical fertilizers containing phosphate and nitrate can pollute waterways, leading to eutrophication. Eutrophication is a process in which excessive nutrients cause algae to grow out of control, which can lead to the death of fish and other aquatic life.
• Human health: Chemical fertilizers containing phosphate and nitrate can also contaminate drinking water, which can lead to health problems such as kidney damage and cancer.

(d) Wastes containing pathogens originated from a health

• Environment: Wastes containing pathogens can contaminate soil and water, which can lead to the spread of disease.
• Human health: Wastes containing pathogens can cause a variety of diseases, such as cholera, typhoid, and dysentery.

(e) Chlorofluorocarbons (CFCs)

• Environment: CFCs are ozone-depleting substances, which means that they can destroy the ozone layer. The ozone layer protects us from harmful ultraviolet radiation from the sun.
• Human health: CFCs can also contribute to climate change.

The ever-increasing population in the different cities of India is creating a crisis of groundwater. It is due to the over-exploitation of natural resources and loss of the ecosystem.Water resources are not sufficient on the earth for such a huge population. So, to fulfil the need of the population, the over-exploitation of natural resources started. Groundwater was used for irrigation, electric energy production and in functions on a large scale. Due to Global warming, the destruction of forests and plants, trees etc. Took place. As a result, natural unbalance, caused a disturbance in the regular Rain – cycle. The ever-increasing population affected the water ecosystem. Therefore, the water became polluted and a crisis of groundwater was created.

Increase in the habitat of People → Urbanization → Road making → Establishment of factories → Use of terrestrial lands → Deforestation → decrease in the habitat of plants and animals Loss of biodiversity Pollution unbalance of the ecosystem of Sunderban

Here are some conservation measures that have been adopted:

1. Establishment of protected areas: Protected areas such as national parks and wildlife sanctuaries have been established to protect the habitat of the hispid hare.
2. Control of hunting and poaching: Hunting and poaching are major threats to the hispid hare, and conservation efforts have focused on controlling these activities.
3. Reintroduction of captive-bred individuals: Captive-bred hispid hares have been reintroduced into the wild in an effort to increase the population.
4. Public awareness: Public awareness campaigns have been launched to educate people about the importance of conserving the hispid hare.

Here are some of the roles of biodiversity in maintaining the balance of the ecosystem of a river:

• Stabilizing river flows: Biodiversity helps to stabilize river flows by providing a variety of plants and animals that help to absorb and release water. This helps to prevent flooding and droughts.
• Filtering pollutants: Biodiversity helps to filter pollutants from river water by providing a habitat for a variety of plants and animals that help to remove pollutants from the water. This helps to keep the water clean and safe for drinking and other uses.