What do you think Earth would look like if there were no life on it at all?
Answer
Without any life, the Earth would look like a barren, rocky planet. There would be no green forests, no animals, and no people. The land would be covered only with rocks, soil, deserts, and water bodies, much like a lifeless planet such as Mars. The air, water, and soil would still be present, but there would be no living beings to make use of them or to keep the natural systems in balance.
Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?
Answer
Life on Earth keeps going mainly because of reproduction. Through reproduction, each type of organism produces new individuals, ensuring the continuity of life. Reproduction also allows small changes in the instructions (genes) passed from parents to offspring. These changes sometimes help living beings adapt and survive better in new or changed environments. This ability to reproduce and adapt allows life to continue even after major changes and disasters.
Why don't dogs lay eggs? Or hens give birth to live chicks?
Answer
This is because different animals follow different ways of developing their young ones. In hens (birds), the fertilised egg is laid by the female, and the development of the embryo takes place inside the egg after it is laid. In dogs (mammals), the development of the young one takes place inside the body of the female, where the mother's body provides all the food and oxygen needed until the baby is born. So each kind of animal reproduces in the way suited to it.
If a spaceship carried soil and water to Mars, could plants start growing there?
Answer
Simply carrying soil and water may not be enough for plants to grow on Mars. Mars lies at the edge of the Sun's habitable zone and its atmosphere is about 100 times thinner than that of the Earth. It also lacks enough oxygen and a suitable temperature. Plants need air, sunlight, water, and the right temperature to grow. So unless these Earth-like conditions are also recreated, plants would not be able to grow naturally on Mars.
What is one major reason Mars cannot currently support life like Earth?
- It has too many volcanoes.
- It is too close to the Sun.
- It lacks a thick atmosphere and liquid water.
- Its magnetic field is too strong.
Answer
It lacks a thick atmosphere and liquid water.
Reason — Liquid water and a suitable atmosphere are essential for life. Mars lies at the edge of the Sun's habitable zone, and its atmosphere is about 100 times thinner than that of the Earth. Because of its small size, Mars has weak gravity, which cannot hold a thick atmosphere. Without a thick atmosphere and liquid water, conditions on Mars cannot support life the way the Earth does.
Mars has volcanoes, but they are not the main reason it cannot support life. Mars is actually farther from the Sun than Earth. Mars has a very weak global magnetic field, not a strong one.
Which of these is an example of geodiversity?
- Variety of bird chirping in a forest.
- Different landforms like mountains, valleys, and deserts.
- Changing weather during monsoons.
- Number of different types of fish in a pond.
Answer
Different landforms like mountains, valleys, and deserts.
Reason — Geodiversity refers to the variety of landforms, rocks, soils, etc., on the Earth, along with the processes that shape and alter them. Different landforms like mountains, valleys, and deserts are examples of this variety. The other options refer to living things (birds, fish) or to weather, which are not part of geodiversity.
Variety of bird chirping is related to living organisms, not geodiversity. Changing weather is an atmospheric process, not geodiversity. Different types of fish are examples of biodiversity (variety of living organisms).
If the Earth were smaller with the same density, what might happen to its atmosphere?
- It would become thicker and hotter.
- It would escape into space due to weaker gravity.
- It would become frozen.
- It would cause stronger winds.
Answer
It would escape into space due to weaker gravity.
Reason — A planet needs enough gravity to hold on to its atmosphere. If the Earth were much smaller (with the same density), its gravity would become too weak to keep the gases bound to it, and the atmosphere would escape into space.
Weaker gravity would not make the atmosphere thicker. A smaller Earth does not automatically freeze the atmosphere. Wind strength depends on many factors and is not a direct consequence of a smaller Earth.
In sexual reproduction, why are offspring different from their parents?
- They grow in different climates.
- They eat different food.
- They acquire new instructions after birth.
- They get mixed instructions (genes) from both parents.
Answer
They get mixed instructions (genes) from both parents.
Reason — In sexual reproduction, instructions from two parents combine to create the offspring. The young one receives a mix of genes from both the mother and the father, so it is not exactly like either parent and shares some traits with each. This mixing is why offspring differ from their parents.
Climate can affect appearance or growth, but it is not the main reason offspring differ genetically from their parents. Food affects growth and health, not the genetic makeup inherited from parents. Genetic instructions are inherited at fertilisation, not acquired after birth.
You notice tiny green plants growing in cracks on your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?
Answer
The seeds were most likely brought to the cracks by wind, insects, birds, or animals. For example, a bird that ate a fruit may have dropped the seed there. After the monsoon rains, the cracks held water and some soil or dust, providing moisture. When the seeds got water, they used their stored nutrients to grow roots and shoots. Along with water, the presence of air and sunlight provided the right conditions for these tiny plants to grow in the cracks.
A city has recently cut down a large patch of forest to build new roads and buildings. Discuss the possible effects this could have on the local climate and biodiversity? How might this affect water availability or quality in the area?
Answer
Cutting down a large patch of forest can affect the area in many ways:
(i) Effect on climate — Trees absorb carbon dioxide and help keep the air cool and clean. Removing them increases carbon dioxide in the air, which can raise the local temperature and disturb rainfall.
(ii) Effect on biodiversity — Forests are home to many plants and animals. When the forest is destroyed, these living beings lose their habitat and may disappear, upsetting the balance of the ecosystem.
(iii) Effect on water — Trees help refill groundwater and keep the water cycle going. Without them, less rainwater soaks into the ground, reducing water availability. Soil and pollutants may also wash into water bodies, lowering the quality of water.
A friend says, "The Earth has always had climate changes in the past, so today's global warming is nothing new." How would you respond using what you've learnt in this and other chapters of your science book?
Answer
It is true that the Earth's climate has changed naturally in the past. However, today's global warming is different because it is happening much faster and is caused mainly by human actions. Burning fossil fuels like coal and oil releases greenhouse gases such as carbon dioxide and methane, which trap extra heat in the atmosphere. This extra carbon was locked underground for millions of years, and the Earth cannot absorb it fast enough. As a result, the temperature is rising quickly, melting ice caps, raising sea levels, and causing extreme weather. So today's global warming is a serious, human-caused problem and cannot be treated as just a natural change.
Imagine Earth's magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.
Answer
The Earth's magnetic field acts like a protective shield. It pushes away harmful, high-energy particles coming from space, such as cosmic rays from the universe and the solar wind from the Sun. If the magnetic field suddenly disappeared, these harmful particles would reach the Earth freely. They could damage the atmosphere, reduce the ozone layer, and let in more harmful ultraviolet (UV) rays. This could harm living cells and put life on Earth at serious risk.
You are tasked with designing a new settlement for humans on Mars. Name three things you would need to recreate from Earth to support human life there. Which of these do you think is the hardest to replicate, and why?
Answer
To support human life on Mars, three important things from Earth would need to be recreated:
(i) A pressurised atmosphere with oxygen — needed for breathing and to maintain suitable pressure inside shelters.
(ii) Liquid water — essential for drinking, growing food, and other life processes.
(iii) A controlled temperature and protection from harmful particles — needed because Mars is very cold and does not have a strong protective atmosphere and magnetic field like Earth.
Among these, recreating an Earth-like atmosphere and protective shield would be the hardest. Mars has weak gravity due to its small size, so it cannot hold a thick atmosphere like Earth, and humans would need protection from harmful high-energy particles from space.
In a village, the temperature has been increasing and rainfall has become unpredictable over the past few years. What could be causing this change? Suggest two ways the village could adapt to these new conditions.
Answer
The rising temperature and unpredictable rainfall are signs of climate change. This is mainly caused by an increase in greenhouse gases such as carbon dioxide in the atmosphere, due to the burning of fossil fuels and the cutting down of trees, which trap more heat.
Two ways the village could adapt are:
(i) Save and store water — by harvesting rainwater and using water carefully so that there is enough during dry periods.
(ii) Change farming practices — by growing drought-resistant crops, adjusting sowing times according to rainfall, and using methods such as drip irrigation to reduce water wastage.
If there were no atmosphere on the Earth, would it affect life, temperature, and water on the planet? Explain.
Answer
Yes, the absence of an atmosphere would badly affect life, temperature, and water on the Earth.
(i) Effect on life — The atmosphere contains oxygen, which humans, animals, and plants need for respiration. Without it, life as we know it could not survive. The atmosphere also has the ozone layer, which blocks harmful UV rays.
(ii) Effect on temperature — Without an atmosphere there would be no greenhouse effect, so the Earth would lose its heat to space and become too cold.
(iii) Effect on water — As the Earth would become too cold, water could not remain in the liquid state, which is essential for life.
Discuss five examples of vegetative propagation.
Answer
Vegetative propagation is a kind of asexual reproduction in which a new plant grows from a part of the plant—like a leaf, stem, or root—planted in soil. Five examples are:
(i) Money plant — A new plant grows from a stem cutting.
(ii) Potato — New plants grow from the 'eyes' (buds) of a sprouted potato.
(iii) Ginger — A new plant grows from a piece of ginger.
(iv) Sugarcane — New plants grow from stem cuttings containing nodes.
(v) Bamboo — New plants grow from its stem parts rather than from seeds.