Test: Basic Biology - Class 10 MCQ

Protoplasm is often described as the "physical basis of life" because it is the living component of the cell, comprising both the cytoplasm and the nucleus. It is inside the protoplasm that all the vital activities such as metabolism, growth, and reproduction occur. The cell wall is a rigid covering, and the nucleus is only one part of the protoplasm, but the entire protoplasm as a whole is responsible for life processes. Hence, it rightly deserves the title of the “living substance.”

Metabolism is a comprehensive word that includes every chemical reaction happening inside a living cell. It has two sides: anabolism, which builds up complex molecules like proteins and starch from simpler ones, and catabolism, which breaks complex molecules down to release energy. Think of metabolism as the grand “bank account” of life processes—some deposits are made (anabolism) while withdrawals are also taken (catabolism). Without metabolism, life would simply not exist.

Living organisms grow by cell division and protoplasm addition. Once a child grows taller, that height cannot be undone; it is permanent. In contrast, when crystals “grow,” they simply deposit more of the same material from outside, and if the conditions change, the crystal may shrink again. Similarly, a balloon may swell, but if the air is removed, it shrinks back. Therefore, true biological growth is irreversible and distinguishes living organisms from non-living things.

When a lizard loses its tail while escaping from a predator, the lost part can grow again. This ability is termed regeneration. It is different from repair, which merely fixes damaged tissues, and from growth, which is an overall increase in body size. Nor is it reproduction, because the lizard is not creating a new organism, only a lost part. Regeneration is nature’s way of giving some organisms a “second chance” when they lose essential body parts.

In respiration, glucose and other organic molecules are broken down with the help of oxygen, releasing carbon dioxide, water, and energy in the form of ATP. Since larger molecules are broken down into smaller ones with energy release, it falls under catabolism. The released energy is then used for all other cellular activities, including anabolic processes like protein synthesis. Thus, respiration is the central catabolic process of life.

Amoeba is a unicellular organism that moves and captures food using extensions of its cytoplasm called pseudopodia, meaning “false feet.” These are temporary projections that flow in the direction of movement. Unlike cilia and flagella, which are permanent structures, pseudopodia can appear and disappear as needed, giving the amoeba remarkable flexibility. This simple form of locomotion also helps it engulf food particles by phagocytosis.

Photosynthesis is the process by which green plants use chlorophyll, sunlight, carbon dioxide, and water to produce glucose and release oxygen. It is the foundation of life on Earth, as it provides the primary source of energy for nearly all organisms, directly or indirectly. Without photosynthesis, there would be no food chain, no oxygen in the atmosphere, and life as we know it would not survive.

Every cell produces waste products like carbon dioxide, urea, and excess water during metabolic reactions. If these harmful substances were allowed to accumulate, they would poison the organism. Excretion ensures that such wastes are removed efficiently. For example, humans excrete urea through urine, plants remove oxygen produced during photosynthesis, and fish excrete ammonia through gills. Thus, excretion is the “sanitation system” of the body.

A stimulus is any change in the environment, such as light, temperature, or touch, that brings about a response in an organism. Plants bending toward light (phototropism) and humans withdrawing their hand from a hot object are classic examples. This capacity to detect and respond is called irritability or sensitivity. Without irritability, organisms would fail to adjust to their surroundings and survival would be at risk.

Metabolism, reproduction, and irritability are fundamental features of life, observed in all living organisms. Crystallization, on the other hand, is a purely physical process where molecules arrange themselves in a regular pattern, as in the growth of sugar crystals. It does not involve cells, energy transformations, or biological regulation, and hence it cannot be considered a living process.

Living organisms maintain a constant internal environment despite external changes. This ability is called homeostasis, such as humans keeping body temperature around 37°C even in hot or cold weather. Non-living things like stones or chairs have shape, colour, and mass, but they cannot regulate their inner conditions. Thus, the absence of homeostasis is a key difference between living and non-living matter.

Non-living things, like crystals, may appear to grow, but their growth is superficial, occurring by the addition of material from outside. Unlike organisms, they lack cells, cannot respond to stimuli, and cannot reproduce. This external mode of “growth” makes non-living things fundamentally different from living organisms, where true growth is internal and irreversible.

When a plant bends towards sunlight, it is showing sensitivity to light, a stimulus from the environment. This response is called phototropism and is a classic example of irritability in plants. Regeneration and pseudopodia movement are growth and locomotion processes, while crystal formation is a physical change, not a biological response.

Metabolism is the umbrella term for all chemical reactions in a cell. It includes catabolism, where complex molecules are broken down to release energy, and anabolism, where simpler molecules are built into complex ones using energy. Respiration is only one catabolic process, but metabolism includes much more, such as protein synthesis, DNA replication, and lipid formation.

Living organisms increase their size and mass by dividing and adding new cells, which is an internal and permanent process. In contrast, crystals “grow” only when more of the same substance deposits on their surface, making the growth reversible. This comparison is often highlighted in ICSE exams to distinguish living from non-living matter.

While processes like nutrition and respiration keep an individual alive, only reproduction ensures that the species as a whole continues to exist. Through sexual or asexual reproduction, organisms produce new individuals that resemble them. Without reproduction, every species would face extinction after the natural death of its members.

Every organism has a definite life span—the total time from birth to natural death. For example, a mayfly may live for only one day, while a banyan tree can live for hundreds of years. Life span is not the same as evolution, which occurs over generations, nor is it a metabolic process.

Non-living things lack the fundamental unit of life—the cell. This is why they cannot perform metabolism, reproduce, or respond to stimuli. They may exist in shapes and sizes, but without cellular organization, they cannot be classified as living.

Adaptation refers to changes over generations that help organisms survive in their environment. Bacteria that survive antibiotic exposure pass on resistant traits, showing evolution in action. Crystals, stones, and balloons undergo physical changes but not biological adaptation.

In nutrition, food must first be taken in (feeding). It is then broken down into simpler, absorbable forms (digestion). Finally, the digested nutrients are absorbed and used by cells for energy and growth (assimilation). This sequence ensures that organisms can use food efficiently to sustain life.