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Practice MCQ Questions for Class 7 Science

1. Sometimes when we do heavy exercise, anaerobic respiration takes place in our muscle cells. What is produced during this process?

(a) alcohol and lactic acid
(b) alcohol and CO₂
(c) lactic acid and CO₂
(d) lactic acid only

2. Yeast is used in wine and beer industries because it respires.

(a) aerobically producing oxygen
(b) aerobically producing alcohol
(c) anaerobically producing alcohol
(d) anaerobically producing CO₂

3. During the process of exhalation, the ribs move

(a) down and inwards
(b) up and inwards
(c) down and outwards
(d) up and outward

4. Breathing is a process that

(i) provides O₂ to the body.
(ii) breaks down food to release energy.
(iii) helps the body to get rid of CO₂
(iv) produces water in the cells.

Which of the following gives the correct combination of functions of breathing?

(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)

5. Which are the gases involved in breathing?

(a) O₂ and NO₂
(b) O₂ and SO₂
(c) O₂ and O₃
(d) O₂ and CO₂

6. Name the organ of the body in which the blood is oxygenated.

(a) Heart
(b) Lungs
(c) Lever
(d) Pancrea

7. Yeasts are used in

(a) wine and beer industry
(b) bakery
(c) in both
(d) none of these

8. Breathing rate in human beings in normal condition is

(a) 12-15 times in a minute
(b) 15-18 times in a minute
(c) 18-22 times in a minute
(d) 22-25 times in a minute

9. The process of breakdown of food in the cell with the release of energy is called ________ 

(a) Respiration 
(b) Inhalation
(c) Exhalation
(d) Breathing

10. Giving out of air rich in carbon dioxide is called __________

(a) Respiration
(b) Inhalation
(c) Exhalation
(d) Breathing

11. To which disease is smoking linked ? 

(a) Appendicitis
(b) Cancer
(c) Fever
(d) Anaemia

12. Name the organism which breathes through its skin 

(a) Cat
(b) Human beings 
(c) Dog
(d) Earthworm

13. The small openings in the body of a cockroach are called

(a) Holes
(b) Spiracles
(c) Tracks
(d) Pores

14. The air tubes that an insect has are useful for the exchange of________

(a) Gases
(b) Liquids
(c) Solids
(d) No exchange

15. The network of air tube in insects for gaseous exchange is called as

(a) Trachea
(b) Spiracles
(c) Stomata
(d) Skin

16. Which of the following is most likely to have a much higher breathing rate?

(a) Man
(b) Dog
(c) Sparrow
(d) Fish

17. The most common substrate for respiration is

(a) fats
(b) amino acids
(c) glucose
(d) sucrose

18. Which part of nose prevents the passage of smoke dust inside the body:

(a) hair
(b) nosal cavity
(c) nostrils
(d) none of these 

19. Muscular floor of the chest cavity is called

(a) Rib cage
(b) Diaphragm
(c) Trachea
(d) Bronchus

20. The organisms which cannot be seen with the naked eyes are called

(a) Plants
(b) Microorganisms
(c) Trachea
(d) Bronchus

21. Oxidation of food inside cell takes place in

(a) Golgi bodies
(b) Mitochondria
(c) Chromosome
(d) Ribosome

22. The chemical used to test the carbon dioxide gas in exhaled air is

(a) Lime water
(b) Limestone
(c) Lime juice
(d) Quick lime

23. A molecule of haemoglobin carries oxygen molecules.

(a) 1
(b) 2
(c) 3
(d) 4  

24. Voice box is present in

(a) Pharynx
(b) Epiglottis
(c) Mouth
(d) Larynx

25. Small thin walled balloon like structure that help in exchange of gases are

(a) Arteries
(b) Veins
(c) Stomata
(d) Alveoli

Answer:

1. Answer: (d) lactic acid only

Explanation: While doing heavy exercise such as running, cycling, weightlifting, etc., we need high energy which creates an impermanent deficiency of oxygen in the muscle cells. In absence of oxygen, our body performs anaerobic respiration in which glucose present in the muscle cells is changed into lactic acid.

2. Answer: (c) anaerobically producing alcohol

Explanation: Yeast respires anaerobically to produce ethanol and CO₂.

3. Answer: (a) down and inwards

Explanation: The procedure of "removing air from the lungs" which is rich in carbon dioxide is termed as exhalation. To remove the air from the lungs move downwards and inwards.

4. Answer: (c) (i) and (iii)

Explanation: Breathing is the process of inhaling oxygen into the body and exhaling carbon dioxide out of the body. It provides O₂ to the body and helps the body to get rid of CO₂.

5. Answer: (d) O₂ and CO₂

Explanation: O₂ and CO₂ are the gases involved in breathing. Breathing is the process of inhalation of oxygen and exhalation of carbon dioxide for respiration.

6. Answer: (b) Lungs

Explanation: The right ventricle pumps the blood to the lungs where it becomes oxygenated. The oxygenated blood is brought back to the heart by the pulmonary veins which enter the left atrium Oxygenation takes place in the lungs.

7. Answer: (a) wine and beer industry

Explanation: Yeast is used in wine and beer industries because it respires Anaerobically producing alcohol.

8. Answer: (b) 15-18 times in a minute

Explanation: Breathing (or ventilation) is the process of moving air into and out of the lungs to facilitate gas exchange with the internal environment, mostly by bringing in oxygen and flushing out carbon dioxide.The Normal range of breathing rate per minute in an average adult person at rest is 15-18.

9. Answer: (a) Respiration 

Explanation: The process of breakdown of food in the cell with the release of energy is called cellular respiration. Cellular respiration takes place in the cells of all organisms.

10. Answer: (c) Exhalation

Explanation: Breathing the physical process of respiration where breathing-in and breathing-out of various gases take place. While exhaling, the carbon dioxide collected from various parts of the body  is the major gas that is thrown out of the body. Since carbon dioxide is one the most abundant waste product formed in the body, the exhaled air is rich in carbon dioxide.

11. Answer: (b) Cancer 

Explanation:Tobacco use causes many types of cancer, including cancer of the lung, larynx (voice box), mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukemia.

12. Answer: (d) Earthworm

Explanation:  Earthworms breathe through their skins. The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. Though frogs have a pair of lungs like human beings, they can also breathe through their skin, which is moist and slippery.

13. Answer: (b) Spiracles

Explanation: In cockroaches, the respiratory system consists of a network of trachea that open outside through small holes that are present on lateral side of the body are called spiracles and are of 10 pairs.

14. Answer: (a) Gases

Explanation: Insects use air-filled tubes called tracheae to exchange oxygen and carbon dioxide between their tissues and the air. This network of tubes is also called a tracheal system. Insect body contains small openings on the outer surface called spiracles. Spiracles are connected to the internal tubes.

15. Answer: (a) Trachea

Explanation: In insects, the respiratory system has a network of the trachea. They are opened through 10 pairs of spiracles that are present on the lateral sides of the body. The trachea has network of air tubes for gaseous exchange.
So the correct answer is 'Trachea'.

16. Answer: (d) Fish

Explanation:The smaller the size of the animal, higher is the metabolic rate and higher the respiratory (breathing) rate. This is because a smaller size means a higher surface area to volume ratio and, therefore, a higher need for oxygen to be supplied to the different tissues. Since fishes are smaller in size they will have a much higher breathing rate.

17. Answer: (c) glucose

Explanation: The various organic substances such as carbohydrates, fats and proteins are respired completely to carbon dioxide and water are called respiratory substrates. Under natural conditions only carbohydrates are used. Glucose being the simplest monosaccharide hexose molecule acts as the chief respiratory substrate.

18. Answer: (a) hair

Explanation: Hairlike structures called cilia line the mucous membrane and move the particles trapped in the mucus out of the nose. Inhaled air is moistened, warmed, and cleansed by the tissue that lines the nasal cavity.

19. Answer: (b) Diaphragm

Explanation: The diaphragm is a large muscular sheet which forms the floor of the chest cavity. It is a domed shaped structure made up of muscles which separate thoracic cavity and abdominal cavity.

20. Answer: (b) Microorganisms

Explanation: The microorganisms are the microscopic bodies which cannot be seen directly with the naked eye. These organisms are of the size in microns. The study which deals with the microbes is known as microbiology. There are the different types of microbes like bacteria, viruses, fungi, etc.

21. Answer: (b) Mitochondria 

Explanation: Mitochondria produces the energy currency, i.e., ATPs of the cell. Mitochondria is the power house of cell. It produces ATP by oxidising nutrients in the cell. This process is known as 'oxidative phosphorylation'. 

22. Answer: (a) Lime water

Explanation: Limewater (calcium hydroxide solution) will turn cloudy/milky when a certain amount of carbon dioxide is passed through it. It is a specific test for carbon dioxide.

23. Answer: (d) 4

Explanation: Each hemoglobin molecules is made of four polypeptide chains, and four oxygen molecules bind to one molecule of hemoglobin.

24. Answer: (d) Larynx

Explanation: Larynx — also known as the voice box, the larynx is a cylindrical grouping of cartilages, muscles and soft tissue that contains the vocal cords. The larynx is the upper opening into the windpipe (trachea), the passageway to the lungs.

25. Answer: (d) Alveoli

Explanation: In lungs, the bronchioles terminate in balloon-like structures called alveoli. The alveoli contains network of blood capillaries that increase the surface area for exchange of gases.

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