Introduction to Cells

Cells are the basic building blocks of all living organisms. They are the smallest units of life and are responsible for carrying out all the essential functions that allow organisms to grow, develop, and survive. Some organisms, like bacteria, are made of just one cell (unicellular), while others, like humans, are made up of trillions of cells (multicellular). Understanding cells helps us learn how life operates at its most fundamental level.

Key Parts of a Cell

1. Cell Membrane: The thin layer that surrounds the cell and controls what goes in and out.
2. Nucleus: Often considered the “control centre” of the cell, containing DNA and directing the cell’s activities.
3. Cytoplasm: A jelly-like substance where most cellular activities occur.
4. Mitochondria: Known as the “powerhouse” of the cell, they generate energy for the cell.
5. Chloroplasts: Found only in plant cells, these structures contain chlorophyll for photosynthesis.
6. Cell Wall: A rigid layer found only in plant cells that provides structure and support.
7. Vacuole: A storage space in cells, larger in plant cells, which holds water, nutrients, and waste.

Types of Cells

1. Animal Cells: These cells have a flexible shape and contain a cell membrane, nucleus, cytoplasm, and mitochondria.
2. Plant Cells: In addition to the structures found in animal cells, plant cells have a cell wall, chloroplasts, and a large vacuole, allowing them to support themselves and carry out photosynthesis.

Exam Questions on Cells

Here are 20 questions each at easy, medium, and hard levels to test your understanding of the topic.

Easy Level Questions

Basic Understanding of Cells

1. What is a cell?
2. What is the function of the cell membrane?
3. Which part of the cell contains DNA?
4. What is the role of mitochondria in a cell?
5. Name one part of a plant cell that is not found in an animal cell.
6. What is cytoplasm?
7. What is the function of the nucleus?
8. Which cell part is responsible for photosynthesis in plants?
9. What is a cell wall?
10. Which cells have chloroplasts: plant cells or animal cells?
11. What is the role of the vacuole in a cell?
12. Which type of cell has a fixed shape, plant or animal?
13. What substance fills the cytoplasm?
14. What is the basic unit of life?
15. What is the main difference between plant and animal cells?
16. What is the ‘powerhouse’ of the cell?
17. What is the outermost layer of a plant cell?
18. What are cells that make up animals called?
19. What is the main purpose of chloroplasts?
20. What do all cells have in common?

Medium Level Questions

Intermediate Knowledge of Cell Structure and Functions

1. Explain the main function of the cell membrane.
2. Describe the role of the nucleus in the cell.
3. How do mitochondria provide energy for the cell?
4. Why do plant cells have a cell wall?
5. Explain the function of chloroplasts in plant cells.
6. What is the function of a vacuole in a plant cell?
7. Describe the role of cytoplasm in the cell.
8. What is the purpose of DNA in the nucleus?
9. How do animal cells differ from plant cells in structure?
10. Explain why plant cells contain chloroplasts but animal cells do not.
11. What is the role of the cell wall in plant cells?
12. Where are proteins made in the cell?
13. How does the structure of a plant cell help it to carry out photosynthesis?
14. Why do plant cells have a large vacuole?
15. Describe the importance of the nucleus in controlling cell activities.
16. What is the function of ribosomes in the cell?
17. Explain why mitochondria are called the ‘powerhouses’ of the cell.
18. How does a cell wall help protect a plant cell?
19. What is the main difference between prokaryotic and eukaryotic cells?
20. What is the purpose of the cell membrane in animal cells?

Hard Level Questions

Advanced Concepts and Applications in Cell Biology

1. Explain how plant cells produce their own food.
2. Describe how DNA controls the activities of a cell.
3. How do cells use energy from mitochondria to perform functions?
4. Explain the importance of the large vacuole in maintaining plant structure.
5. Describe the process of photosynthesis and where it occurs in the cell.
6. Explain why animal cells do not need chloroplasts.
7. What is the role of specialised cells in multicellular organisms?
8. How does the cell membrane regulate the movement of substances?
9. Describe the role of ribosomes in protein synthesis.
10. Explain the difference between osmosis and diffusion in cells.
11. How do chloroplasts and mitochondria work together in plant cells?
12. Describe how cells in multicellular organisms are organised into tissues and organs.
13. Explain why plant cells have a fixed shape, but animal cells do not.
14. How does the structure of a red blood cell help its function?
15. Describe how the cell wall and cell membrane work together in plant cells.
16. What is cell division, and why is it important for growth?
17. Explain the role of lysosomes in animal cells.
18. How does cell differentiation lead to specialised cell functions?
19. Describe the process of respiration in mitochondria.
20. Explain why nerve cells have long extensions.

Answers and Explanations

Easy Level Answers

1. The basic unit of life – Cells are the building blocks of all living things.
2. Controls what enters and leaves the cell – The cell membrane acts as a gatekeeper.
3. The nucleus – Contains genetic material (DNA).
4. Generates energy for the cell – Mitochondria produce energy.
5. Chloroplasts or cell wall – These are found only in plant cells.
6. A jelly-like substance in the cell – Cytoplasm fills the cell and holds organelles.
7. Controls the cell’s activities – The nucleus acts as the cell’s command centre.
8. To perform photosynthesis – Chloroplasts help make food for the plant.
9. A rigid outer layer in plant cells – The cell wall provides structure and support.
10. Plant cells – Only plant cells contain chloroplasts.
11. Stores water, nutrients, and waste – The vacuole is a storage organelle.
12. Plant cells – Have a fixed shape due to the cell wall.
13. A jelly-like substance – The cytoplasm contains various molecules.
14. The cell – Cells are the smallest units of life.
15. Plant cells have a cell wall and chloroplasts – Animal cells do not have these.
16. Mitochondria – Known as the cell’s powerhouse.
17. The cell wall – Provides support and protection.
18. Animal cells – Cells that form animals.
19. To carry out photosynthesis – Chloroplasts help plants make food.
20. Cell membrane, cytoplasm, and genetic material – All cells have these basic structures.

Medium Level Answers

1. Regulates entry and exit of substances – Maintains the internal environment of the cell.
2. Holds DNA and directs cell activities – The nucleus is the control centre.
3. Mitochondria produce energy through respiration – They break down glucose to release energy.
4. Provides support and shape – The cell wall helps the plant stand upright.
5. Chloroplasts capture sunlight for photosynthesis – They produce food for the plant.
6. Stores water, nutrients, and waste – The vacuole keeps the cell hydrated.
7. Holds organelles and allows chemical reactions – Cytoplasm supports cell functions.
8. DNA carries genetic instructions – Controls traits and cell activities.
9. Animal cells lack a cell wall and chloroplasts – Plant cells have these structures.
10. Plants make food using sunlight – Chloroplasts capture sunlight for this purpose.
11. Provides structural support – The cell wall protects and strengthens the cell.
12. In ribosomes – Proteins are made here.
13. Chloroplasts use sunlight to create food – The cell wall and vacuole support this process.
14. Helps maintain cell shape by holding water – The vacuole supports the cell.
15. Controls activities like growth and reproduction – The nucleus is essential for cell function.
16. Builds proteins needed by the cell – Ribosomes are protein factories.
17. Produce energy for cell activities – Mitochondria power the cell.
18. **Provides structure and protection

** – The cell wall is strong and rigid.

19. Prokaryotic cells lack a nucleus; eukaryotic cells have one – Fundamental difference in cell types.
20. Regulates entry and exit of materials – The cell membrane controls what moves in and out.

Hard Level Answers

1. Use chloroplasts to capture sunlight and make food – Plants produce food through photosynthesis.
2. DNA codes for proteins that control cell functions – DNA provides instructions for cell activities.
3. Mitochondria release energy for cell functions – Energy is needed for growth and repair.
4. Stores water, keeping the plant firm – The vacuole helps support the plant.
5. Photosynthesis converts sunlight to food – This occurs in chloroplasts in plant cells.
6. Animals get food from their diet – They don’t need chloroplasts to make food.
7. Perform specific tasks, like muscle or nerve cells – Specialised cells carry out unique functions.
8. Allows only certain substances to enter – The cell membrane is selectively permeable.
9. Ribosomes create proteins from amino acids – Protein synthesis occurs here.
10. Osmosis is water movement; diffusion is other particles – Both move substances across membranes.
11. Chloroplasts make food; mitochondria release energy – They work together in plant cells.
12. Cells form tissues, which form organs – Specialised cells group into organs.
13. The cell wall keeps the shape stable – Animal cells are more flexible.
14. Shape allows it to carry oxygen – Red blood cells have a large surface area.
15. The cell wall gives shape; the membrane regulates entry – They work together for structure and control.
16. Cells divide to grow and repair tissues – Cell division is essential for growth.
17. Break down waste in animal cells – Lysosomes help keep the cell clean.
18. Cells develop unique shapes for functions – This process is called differentiation.
19. Respiration releases energy from food – This happens in mitochondria.
20. Extensions transmit signals over long distances – Nerve cells are adapted for communication.

These questions and answers help Year 7 students build a thorough understanding of cell biology, covering basic structures, functions, and specialised cell processes. This will prepare them effectively for their Key Stage 3 exams.