Madhyamik Class 10 Life Science Solved Paper 2020
LIFE SCIENCE
Time: 3 Hours and 15 Minutes
(First 15 Minutes for reading the question paper only, 3 Hours for writing)
Full Marks: For Regular Candidates – 90
For External Candidates – 100
Regular candidates will answer questions from Groups A, B, C and D. External candidates will answer questions from Group E.
(Special Instructions for visually handicapped candidates)
Answer Question 4.1(A) instead of Question 4.1 in Group D. Instruction on how many questions from a group must be attempted is provided at the beginning of the group.
Group ‘A’
(All questions are compulsory)
1. Choose the correct answer for each question and write it with its respective-serial number: [1 × 15=15]
Question 1.1
The tentacles on the leaves of an insectivorous plant, called sundew to bend to trap the insect as soon as they come in contact with the insect body. This is —
- Seismonasty
- Thermonasty
- Photonasty
- Chemonasty
Answer
(d) Chemonasty
Question 1.2
In case of women, the Follicle Stimulating Hormone stimulates the Graafian Follicle of the Ovary to secrete the hormone is —
- TSH
- ADH
- Oestrogen
- ACTH
Answer
(C) Oestrogen
Question 1.3
Which one of the following is the correct reflex?
- Receptor → Effector → Efferent nerve → Nerve centre → Afferent nerve
- Nerve centre → Receptor → Afferent nerve → Effector → Efferent nerve
- Efferent nerve → Receptor → Afferent nerve → Nerve centre → Effector
- Receptor → Afferent nerve → Nerve centre → Efferent nerve → Effector
Answer
(d) Receptor → Afferent nerve → Nerve centre → Efferent nerve → Effector
Question 1.4
In which stage of mitosis cell division, the nuclear membrane and nucleolus are seen to disappear
- Anaphase
- Prophase
- Metaphase
- Telophase
Answer
(b) Prophase
Question 1.5
Which of the following is not a structural component of DNA —
- Deoxyribose sugar
- Uracil base
- Thymine base
- phosphoric Acid
Answer
(b) Uracil base
Question 1.6
Which one of the following statements is correct regarding sexual reproduction—
- Haploid gamete formation is essential in sexual reproduction
- Sexual reproduction depends only on mitosis
- In sexual reproduction, offspring could be produced from a single parental organism
- The offsprings produced in sexual reproduction are genetically identical to parental organism
Answer
(a) Haploid gamete formation is essential in sexual reproduction
Question 1.7
Which one of the following is the genotypic ratio at F2 generation of Mendel’s monohybrid cross —
- 1 : 2 :1
- 3 : 1
- 9 : 3 : 3 : 1
- 2 : 1 : 2
Answer
(a) 1 : 2 :1
Question 1.8
Which one of the following is not controlled by the autosomal gene of human —
- Roller tongue
- Hemophilia
- Thalassemia
- Attached ear lobe
Answer
(b) Hemophilia
Question 1.9
What would be the phenotypic ratio in the F2 generation of a monohybrid cross in case of incomplete dominance —
- 3:1
- 2:1:1
- 9:3:3:1
- 1:2:1
Answer
(d) 1:2:1
Question 1.10
Which one of the following is the intraspecific struggle for the same food —
- struggle between Vulture and Hyaena
- struggle between Eagle and Kite
- struggle among the members of Rohu fish in the pond
- struggle between Egret and Kingfisher
Answer
(c) struggle among the members of Rohu fish in the pond
Question 1.11
Which of the following changes did not occur during the course of the evolution of horse —
- Lengthening of limbs
- Increase in the length and thickness of all digits in limbs
- Increase in the length and thickness of only the third digit in limbs
- Increase in size of the -whole body
Answer
(d) Increase in size of the -whole body
Question 1.12
According to the opinion of scientists the prebiotic Environment of the earth that led to the origin of life was like —
- Hot dilute. soup in tie seawater
- Cold dilute soup in the seawater
- Cold dilute soup in the river water
- Hot dilute soup in the groundwater
Answer
(a) Hot dilute. soup in tie seawater
Question 1.13
Which one of the following microbes takes part in nitrification?
- Nitrosomonas
- Azotobacter
- Pseudomonas
- Thiobacillus
Answer
(a) Nitrosomonas
Question 1.14
An example of Ex-situ conservation is
- Sundarbans Tiger Reserve
- Corbet National Park
- Nilgiri Biosphere Reserve
- Cryopreservation
Answer
(d) Cryopreservation
Question 1.15
Which of the following effect is the result of water pollution—
- Global warming
- Eutrophication
- Deafness
- Bronchitis
Answer
(b) Eutrophication
Group B
Answer 21 questions out of 26 questions given below as instructed. [1×21=21]
Fill in the blanks (any five) [1 × 5=5]
Question 2.1
Due to a deficiency of Iodine, the synthesis of hormones is hampered ____
Answer
Thyroid
Question 2.2
During embryonic development and growth in vertebrates ____ cell division take place.
Answer
Mitosis
Question 2.3
The differences of Pea Plant may show the same Phenotype ____
Answer
Genotype
Question 2.4
Homologous organs evolve due to ____ evolution.
Answer
Divergent
Question 2.5
The name of one exotic species, that affects the local biodiversity, is the ____.
Answer
Amazon sailfin catfish
Question 2.6
The fine droplets of smoke, ashes, dust, pollen grains etc., suspended in the air are collectively called ____, which causes various lung diseases.
Answer
Air pollution
Decide whether the following statements are true or false (any five)
Question 2.7
Hypothalamus helps to maintain body balance in humans.
Answer
True.
Explanation:
The hypothalamus plays a crucial role in maintaining body balance in humans by regulating various physiological processes such as body temperature, hunger and thirst, sleep-wake cycles, hormone release, and overall homeostasis.
Question 2.8
In DNA, Adenine is linked with Guanine by hydrogen bonds.
Answer
False.
Explanation:
In DNA, adenine (A) is always paired with thymine (T) by two hydrogen bonds, and guanine (G) is always paired with cytosine (C) by three hydrogen bonds.
Question 2.9
In his monohybrid cross experiment, Mendel obtained 75% pure tall Pea Plants in the first filial generation.
Answer
False.
Explanation:
In his monohybrid cross experiments, Mendel obtained a 100% pure tall phenotype in the first filial generation (F1) because he crossed pure tall (dominant) plants with pure short (recessive) plants. The F1 generation showed the dominant trait exclusively.
Question 2.10
In Lamarck’s opinion, organisms can acquire any particular inheritable physical trait according to their need.
Answer
False.
Explanation:
According to Lamarck’s theory of evolution, organisms can acquire certain traits during their lifetime through use and disuse, and these acquired traits can be passed on to their offspring.
Question 2.11
Acid rain is caused by SO2 and NO2 gases formed due to air pollution.
Answer
True.
Explanation:
Acid rain is primarily caused by the emission of sulfur dioxide (SO2) and nitrogen dioxide (NO2) gases into the atmosphere due to human activities, particularly the burning of fossil fuels.
Question 2.12
Auxin helps the seed to germinate by breaking of dormancy.
Answer
True.
Explanation:
Auxin is a plant hormone that helps in seed germination by breaking dormancy and promoting cell elongation and growth.
Match the right column with the left column: (Any five):
| Column A | Column B |
| 2.13) CSF | a) Large colloidal aggregates |
| 2.14) Crossing over | b) Active participation of local peoples in the restoration of forests. |
| 2.15) Haemophilia | c) Meiosis |
| 2.16) Coacervate | d) Movement of daughter chromosomes towards the poles |
| 2.17) JFM | e) The disorder is caused by a recessive gene located in human X-chromosomes |
| 2.18) Grafting | f) Supplies nutrients to brain cells |
| g) Stock and scion |
Answer
2.13 – (f). 2.14 – (c). 2.15 – (e), 2.16 – (a), 2.17 – (b), 2.18 – (g)
Answer in a single word or in a single sentence (any six) :
Question 2.19
Choose the odd one and write it:
Dwarfism, Goiter, Thalassemia, Diabetes, Mellitus
Answer
Thalassemia
Question 2.20
Mention one function of the lens of the human eyeball
Answer
The Lens of the eyeball helps to focus the light onto the retina.
Question 2.21
A pair of related terms is given below. On the basis of the relationship in the first pair write the suitable word in the gap of the second pair.
Mitosis: Radicle:: ____ : spore mother cell
Answer
Meiosis
Question 2.22
In the case of guineapig whether the phenotype of the two genotypes bbRR and bbRr is same?
Answer
No, in the case of the Guinea pig, the phenotype of the two genotypes bbRR and bbRr is not the same.
Question 2.23
Write the phenotypic ratio obtained in the F2 generation of Mendel’s dihybrid cross experiment.
Answer
The phenotypic ratio obtained in the F2 generation of Mendel’s dihybrid cross experiment is 9:3:3:1.
Question 2.24
Mention one adaptation of the Sundari plant for salt tolerance
Answer
The salt gland on the surface of the leaves secrete salt. Old leaves may store salt.
Question 2.25
Among the following four terms, one includes the other three. Find out that term and write it:
Overall knowledge regarding local biological resources, PBR, Traditional beliefs regarding local biological resources, Sustainable use of local biological resource
Answer
PBR or the “ people’s Biodiversity Registers” is the term that includes the two.
Question 2.26
Name one endangered animal conserved at Singalila National Park.
Answer
The red panda is one of the endangered animals conserved at Singalila National Park.
Group C
3. Answer any 12 questions in 2-3 sentences out of 17 questions given below : [2×12=24]
Question 3.1
Reflex actions occur when the following incidents- happen in the everyday life of humans. Write the importance of these two reflex actions.
- When food particles enter the trachea
- When foreign particles enter the nasal cavity
Answer
- The cough reflex helps to expel the food particles from the trachea and prevent choking.
- The sneeze reflex helps to expel the foreign particles from the nasal cavity and prevent irritation of the airways.
Question 3.2
For correction of which defects in vision of eye spectacles of convex and concave lenses are used?
Answer
A Convex lens is used to remove the defect of Hypermetropia.
A concave lens is used to remove the defect of Myopia.
Question 3.3
List the names of the hormones related to the following functions:
- Regulation of sugar level in blood
- Stimulation for the secretion of hormones from the Thyroid gland.
- Causing the growth of the Corpus Luteum and stimulating the secretion of Progesterone hormone in the female body
- Increasing blood pressure due to anxiety
Answer
- Insulin
- Thyroid Stimulating hormone.
- Luteinizing Hormone
- Adrenaline
Question 3.4
A resting animal attempts to move. Mention four probable reasons behind it.
Answer
A resting animal attempts to move for these four probable reasons as given below:
- To find food and water
- In search of a suitable habitat
- To escape from predators
- In search of a mate.
Question 3.5
Distinguish between autosomes and sex chromosomes of humans based on the following features.
- Nature
- Number
Answer
| Feature | Autosomes | Sex chromosomes |
|---|---|---|
| Nature | Somatic chromosomes | Sex chromosomes |
| Number | 22 pairs (44 chromosomes) | 1 pair (2 chromosomes) |
Question 3.6
What are the processes of asexual reproduction in spirogyra and planaria?
Answer
| Organism | Process | Description |
|---|---|---|
| Spirogyra | Fragmentation | The filament breaks up into small pieces, each of which can grow into a new Spirogyra filament. |
| Spirogyra | Budding | A small bulge forms on the side of the parent filament. The bulge grows and eventually separates from the parent filament, forming a new Spirogyra filament. |
| Planaria | Regeneration | A planarian can be cut into pieces, and each piece can regenerate into a new planaria. |
Question 3.7
Mention two changes related to vision and bones in late adulthood or the senescence phase of human development.
Answer
Here are two changes related to vision and bones in late adulthood or the senescence phase of human development:
- Vision: The lens of the eye becomes less elastic, making it harder to focus on near objects. This is called presbyopia.
- Bones: Bones become less dense and more brittle, making them more likely to break. This is called osteoporosis.
Question 3.8.
With the help of a cross show how the sex of the offspring of humans is determined.
Answer
Sex determination in human
Sex determination is the process by which an individual is identified as male or female. In humans and most animals, sex is determined by the presence or absence of specific sex chromosomes. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome determines maleness, while the absence of it results in femaleness. In some species, environmental factors may also play a role in sex determination. For example, in some reptiles, the temperature of the egg incubation determines the sex of the offspring.
Question 3.9
One day students read an article in newspaper on Thalassemia and were very scared, to know the fate of a thalassemic patient. Write what kind of measures they can take to eradicate this disease from the population.
Answer
Here are some measures that students can take to eradicate thalassemia from the population:
- Get educated about thalassemia.
- Support organizations that are working to eradicate thalassemia.
- Get involved in genetic screening programs.
- Improve access to genetic counselling and testing.
By taking these steps, we can work together to eradicate thalassemia from the population and improve the quality of life for those who are affected by this disease.
Question 3.10
What are all probable gametes to be produced from the hybrid plant YyRr produced at F1 generation in a dihybrid cross-experiment?
Answer
The gametes produced will be YR, Yr, yR, and yr.
Question 3.11
What are the two adaptive significances of air sacs of pigeon?
Answer
The two adaptive significance of air sacs for pigeons are:
- Air sacs are air-filled cavities which help the bird in flight.
- There are two separate sets of sacs and such a network of sacs reduces the specific gravity of the body of birds making them light.
Question 3.12
Write the names of one each vestigial organ present in the vertebral column and alimentary canal in the human body.
Answer
The names of one each vestigial organ present in the vertebral column and alimentary canal in the human body:
- Vertebral column: Coccyx
- Alimentary canal: Appendix
Question 3.13
Write in chronological sequence the names of four main fossil ancestors during the course of evolution of the horse.
Answer
Mesohippus – Merychippus – Pliohippus – Equus
Question 3.14
“Nitrogen cycle is affected due to human activities” state two phenomena to justify it.
Answer
Here are two phenomena that justify the statement that the nitrogen cycle is affected due to human activities:
- Nitrogen fixation: This is the process by which nitrogen gas is converted into a form that can be used by plants. Human activities that increase nitrogen fixation include the use of nitrogen fertilizers and the burning of fossil fuels.
- Nitrogen deposition: This is the process by which nitrogen is deposited from the atmosphere onto the Earth’s surface. Human activities that increase nitrogen deposition include the use of nitrogen fertilizers and the burning of fossil fuels.
Question 3.15
What would be the environmental consequences as a result of recurrent destruction of wetlands and depletion of the quantity of agricultural lands?
Answer
The environmental consequences as a result of recurrent destruction of wetlands and depletion of the quantity of agricultural lands:
- Habitat loss: Wetlands and agricultural lands provide homes for many plants and animals. Their destruction can lead to the loss of these habitats and the species that depend on them.
- Water pollution: Wetlands and agricultural lands help to filter pollutants from water. Their destruction can lead to water pollution, which can have a negative impact on drinking water, aquatic ecosystems, and human health.
- Increased risk of flooding: Wetlands help to absorb floodwaters. Their destruction can increase the risk of flooding, which can damage property and infrastructure.
Question 3.16
What are the harmful impacts sound pollution can exert on the ears and heart in the human body?
Answer
Here are the harmful impacts that sound pollution can exert on the ears and heart in the human body :
Ears:
- Noise-induced hearing loss (NIHL) is the most common health problem caused by sound pollution.
- NIHL can be temporary or permanent, and it can range from mild to severe.
Heart:
- Long-term exposure to loud noise can increase the risk of heart disease.
- This is because noise pollution can raise blood pressure, increase stress hormone levels, and disrupt sleep.
Question 3.17
Mention the roles of biodiversity in the following two aspects in the progress of human civilization:
- Production of foods
- Manufacturing of medicines
Answer
Here are the roles of biodiversity in the production of food and the manufacturing of medicines:
- Production of foods: Biodiversity provides the genetic diversity that is essential for crop improvement. This diversity can be used to develop new varieties of crops that are resistant to pests and diseases, tolerant of drought and other environmental stresses, and nutritious.
- Manufacturing of medicines: Many medicines are derived from plants, animals, and microbes. For example, aspirin is derived from the bark of the willow tree, and quinine is derived from the bark of the cinchona tree.
Group – D
[Long Answer Type Questions]
4. Answer 6 questions or their alternative given below. Sightless candidates have to answer Question No 4.1.(A) instead of 4.1. [5×6=30]
Question 4.1
Draw a diagram of a reflex arc and label the following parts : [3+2=5]
- Receptor
- Sensory nerve
- Nerve centre
- Motor nerve
Answer
OR
Draw the morphology of an ideal eukaryotic chromosome and label the following parts: [3+2=5]
- Chromatid
- Centromere
- Nucleolar Organizer
- Telomere.
Answer
Question 4.1 (A)
Write the name of three structural parts of a reflex arc. Write functions of sensory and motor nerves. [3+2=5]
Answer
Here are the three structural parts of a reflex arc and the functions of sensory and motor nerves:
- Sensory neuron: Carries information from the sense organ to the spinal cord.
- Interneuron: Relays information between the sensory neuron and the motor neuron.
- Motor neuron: Carries information from the spinal cord to the effector organ.
The sensory neuron detects a stimulus and sends an electrical impulse to the spinal cord. The interneuron then relays this impulse to the motor neuron, which sends an impulse to the effector organ, causing it to respond.
The sensory neuron is responsible for carrying information about the environment to the central nervous system. The motor neuron is responsible for carrying information from the central nervous system to the muscles, causing them to contract or relax.
OR
Write the names of three structural parts found in the morphology of an ideal eukaryotic chromosome. Write one function for each of the Centromere and Telomere. [3+2=5]
Answer
- Centromere: Holds the 2 sister chromatids together.
- Telomere: Protects the chromosome from damage.
- Nucleosome: Basic unit of chromatin.
Centromere and telomere are responsible for the segregation of chromosomes during cell division and for protecting the chromosomes from damage, respectively.
Question 4.2
What types of chemical components are synthesized in different stages of Interphase in a cell cycle? What might happen if normal control at different points of a cell cycle is lost? [3+2=5]
Answer
Here are the types of chemical components that are synthesized in different stages of Interphase in a cell cycle:
- G1: DNA repair, proteins, and organelles are synthesized. If normal control is lost in G1, the cell may enter the cell cycle prematurely or may not enter the cell cycle at all.
- S: DNA is synthesized. If normal control is lost in S, the cell may not synthesize DNA correctly, which can lead to errors in cell division.
- G2: Proteins and organelles are synthesized. If normal control is lost in G2, the cell may not be able to divide properly.
If normal control at different points of a cell cycle is lost, it can lead to a number of problems, including:
- Cell growth: The cell may grow too large or too small.
- Cell division: The cell may divide incorrectly, which can lead to errors in the DNA.
- Cancer: Cancer can occur if cells divide uncontrollably.
OR
Depict the alternation of generation in a fern with the help of a flowchart. “In case of Prophase and Telophase changes of opposite nature happens” － Write two such changes. [3+2=5]
Answer
Alternation of generation
The two changes that happen in opposite natures in prophase and telophase:
- Chromosomes condense in prophase and decondense in telophase.
- The nuclear envelope breaks down in prophase and reforms in telophase.
Question 4.3
Colour or seed and shape of seed of a pea plant – taking these two characters Mendel performed a dihybrid cross. Write the genotypes of pea plants having yellow and round seeds produced in the F2 generation of this experiment. State the law of Independent Assortment of Mendel. [2+3=5]
Answer
The genotypes of pea plants having yellow and round seeds produced in the F2 generation of Mendel’s dihybrid cross are:
- YYRR: This genotype is homozygous dominant for both seed colour and seed shape.
- YyRR: This genotype is heterozygous dominant for seed colour and homozygous dominant for seed shape.
- YYRr: This genotype is homozygous dominant for seed colour and heterozygous for seed shape.
- YyRr: This genotype is heterozygous dominant for both seed colour and seed shape.
The law of independent assortment of Mendel states that genes for different traits are inherited independently of each other. This means that the probability of inheriting a dominant allele for one trait does not affect the probability of inheriting a dominant allele for another trait.
OR
State the opposite traits for each of the characters of flowers of pea plant chosen by Mendel for his experiment. “For developing the scientific ideas on heredity the experiments performed by Mendel on pea plants are epochmaking.” － Mention three reasons behind his success in performing these experiments. [2+3=5]
Answer
Seven contrasting characters of the pea plant were selected by Mendel.
| Characteristics | Dominant | Recessive |
| 1. Stem | Tall | Dwarf |
| 2. Seed surface | Smooth | Wrinkled |
| 3. Colour of seed coast | Grey-brown | White |
| 4. Cotyledon | Yellow | Green |
| 5. Flower position | Axial | Terminal |
| 6. Unripepods | Green | Yellow |
| 7. Ripe pods | Inflated | constricted |
Three reasons behind his success in performing these experiments:
- Mendel chose the pea plant because it is a self-pollinating plant. This means that he could control the pollination process and ensure that the parents of the next generation were true-breeding for the traits he was studying.
- The pea plant has easily observable traits. This made it easy for Mendel to track the inheritance of the traits from one generation to the next.
- The pea plant has a relatively short generation time. This allowed Mendel to conduct multiple generations of experiments in a relatively short period of time.
