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Practice Class 7 Science MCQs on respiration, carbon dioxide, hemoglobin, red blood cells, phloem, transpiration, pulse rate, blood circulation, and plant transport with detailed explanations.
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Q1. Exhaled air contains a higher percentage of:
Correct Answer: Carbon dioxide
Detailed Explanation:
Respiration is the process by which living organisms obtain energy from food. During respiration, oxygen is taken into the body and used by cells to break down glucose and release energy. As a result of this process, carbon dioxide and water are produced as waste products.
When we inhale air, it contains about 21% oxygen and only a small amount of carbon dioxide. Inside the lungs, oxygen passes into the bloodstream and is transported to body cells. At the same time, carbon dioxide produced by cells enters the blood and is carried back to the lungs. This carbon dioxide is then removed from the body when we exhale.
Therefore, exhaled air contains a much higher percentage of carbon dioxide than inhaled air. This difference can be demonstrated through the lime water experiment. When exhaled air is passed through lime water, it turns milky because of the increased amount of carbon dioxide present.
Respiration occurs continuously in humans, animals, and even plants. Without oxygen, cells cannot produce the energy needed for growth, movement, and other life processes.
Understanding the composition of inhaled and exhaled air helps students understand how the respiratory system works and why breathing is essential for survival.
Real-Life Examples:
- Breathing out after physical exercise releases more carbon dioxide.
- Lime water turns milky when exhaled air is passed through it.
- Carbon dioxide is removed from the body through the lungs.
Important NCERT Points:
- Oxygen is used during respiration.
- Carbon dioxide is produced as a waste product.
- Exhaled air contains more carbon dioxide.
- Respiration releases energy from food.
Exam-Oriented Fact:
Exhaled air contains significantly more carbon dioxide than inhaled air.
Quick Revision Line:
Carbon dioxide is the gas present in a higher percentage in exhaled air.
Q2. Hemoglobin is present in which blood cells?
Correct Answer: Red Blood Cells (RBC)
Detailed Explanation:
Hemoglobin is a special iron-containing protein found inside red blood cells (RBCs). It gives blood its characteristic red color and performs the important function of transporting oxygen throughout the body.
When blood passes through the lungs, hemoglobin combines with oxygen. The oxygen-rich blood is then transported to different body tissues and organs. Cells use this oxygen to release energy from food through respiration.
After delivering oxygen, hemoglobin also helps transport a portion of the carbon dioxide produced by body cells back to the lungs for removal.
Red blood cells are specially designed for this task. Their biconcave shape provides a large surface area for oxygen absorption, and they lack a nucleus, allowing more space for hemoglobin.
A deficiency of hemoglobin can lead to anemia, a condition in which the body receives less oxygen than required. Symptoms may include tiredness, weakness, and shortness of breath.
Understanding hemoglobin helps students learn how blood supports respiration and supplies oxygen to every part of the body.
Real-Life Examples:
- Hemoglobin carries oxygen during breathing.
- Blood tests often measure hemoglobin levels.
- Athletes require healthy hemoglobin levels for better performance.
Important NCERT Points:
- Hemoglobin is present in RBCs.
- It transports oxygen.
- It contains iron.
- It gives blood its red color.
Exam-Oriented Fact:
Red blood cells are often called oxygen carriers because of hemoglobin.
Quick Revision Line:
Hemoglobin is the oxygen-carrying pigment found in red blood cells.
Q3. In plants, food is transported by the:
Correct Answer: B) Phloem
Detailed Explanation:
Plants prepare their own food through photosynthesis, mainly in the leaves. Once food is produced, it must be transported to all parts of the plant, including roots, stems, flowers, and fruits. This transportation is carried out by a specialized tissue called phloem.
Phloem is made up of living cells that transport prepared food, mainly sugars, from the leaves to other parts of the plant. This movement of food is called translocation.
Unlike xylem, which mainly transports water and minerals upward from the roots, phloem can transport food in both upward and downward directions depending on the plant’s needs.
Food transported through phloem supports growth, storage, flowering, fruit development, and repair of damaged tissues. Without phloem, different parts of the plant would not receive the nutrients required for survival.
The transport system of plants is an excellent example of how living organisms distribute essential substances efficiently.
Real-Life Examples:
- Sugar produced in leaves reaches roots through phloem.
- Fruits receive nutrients through phloem transport.
- Growing plant parts depend on phloem for food supply.
Important NCERT Points:
- Phloem transports food.
- Food is prepared in leaves.
- Transport of food is called translocation.
- Phloem consists of living cells.
Exam-Oriented Fact:
Xylem carries water, while phloem carries food.
Quick Revision Line:
Phloem transports prepared food from leaves to all parts of the plant.
Q4. The evaporation of water from leaves is called:
Correct Answer: Transpiration
Detailed Explanation:
Transpiration is the process by which water evaporates from the surface of leaves into the atmosphere. Most of this water escapes through tiny pores called stomata, which are present mainly on the lower surface of leaves.
Plants absorb water from the soil through their roots. This water travels upward through xylem vessels to different parts of the plant. A significant amount of this absorbed water is eventually lost through transpiration.
Transpiration serves several important functions. It helps cool the plant during hot weather, creates a pulling force that aids the upward movement of water, and maintains the flow of minerals from roots to leaves.
The rate of transpiration depends on environmental factors such as temperature, humidity, sunlight, and wind speed. Hot and windy conditions usually increase transpiration.
Although water loss may seem wasteful, transpiration is essential for the proper functioning and survival of plants.
Real-Life Examples:
- Leaves release water vapor into the air.
- Plants lose more water on hot days.
- Trees help increase atmospheric humidity through transpiration.
Important NCERT Points:
- Water escapes mainly through stomata.
- Transpiration helps cool the plant.
- It assists water transport.
- It is an essential plant process.
Exam-Oriented Fact:
Stomata are the main sites of transpiration in plants.
Quick Revision Line:
Transpiration is the loss of water vapor from plant leaves.
Q5. Pulse rate is measured from the:
Correct Answer: Arteries
Detailed Explanation:
The pulse is the rhythmic expansion and contraction of arteries caused by the pumping action of the heart. Every time the heart beats, blood is pushed into the arteries, creating a pressure wave that can be felt as a pulse.
Pulse rate refers to the number of pulse beats per minute and usually corresponds to the heart rate. In healthy adults, the resting pulse rate is generally between 60 and 100 beats per minute.
The pulse is commonly measured at locations where arteries are close to the skin surface, such as the wrist, neck, or side of the thumb.
Doctors often check pulse rate to assess a person’s cardiovascular health. Physical exercise, excitement, fever, and stress can increase pulse rate, while relaxation and sleep usually decrease it.
Monitoring pulse rate provides valuable information about how effectively the heart is functioning and whether the body is receiving an adequate blood supply.
Real-Life Examples:
- Doctors check pulse during medical examinations.
- Athletes monitor pulse during workouts.
- Pulse rate increases during running or exercise.
Important NCERT Points:
- Pulse is caused by heartbeats.
- Pulse is felt in arteries.
- Pulse rate usually equals heart rate.
- It helps assess heart health.
Exam-Oriented Fact:
The pulse is commonly measured at the wrist where an artery lies close to the skin.
Quick Revision Line:
Pulse rate is measured from arteries and reflects the heartbeat rate.
Chapter Summary:
During respiration, exhaled air contains more carbon dioxide than inhaled air. Hemoglobin present in red blood cells carries oxygen throughout the body. In plants, food is transported by phloem tissue. The evaporation of water from leaves is called transpiration and helps in water transport. Pulse rate is measured from arteries and indicates the activity of the heart. These concepts are important for understanding respiration, circulation, and transport systems in living organisms and are frequently asked in Class 7 Science examinations.
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