Cell Structure and Functions
Focused last-minute revision notes with clear concepts, exam traps, key comparisons and compact practice.
Chapter Snapshot
- The cell is the basic structural and functional unit of life.
- Robert Hooke used the term cell after observing cork under a microscope.
- Organisms may be unicellular or multicellular.
- Cells vary greatly in shape and size according to function.
- Main cell parts include cell membrane, cytoplasm and nucleus.
- Plant cells also have a cell wall and usually a large central vacuole; green cells contain chloroplasts.
- The nucleus contains chromosomes, which carry genes.
- Cells form tissues, tissues form organs and organs work together in organ systems.
What You Will Learn
- Define cell and distinguish unicellular/multicellular organisms
- Relate cell shape to function
- Identify major cell structures
- Compare plant and animal cells
- Explain nucleus, chromosome and gene relationship
- Recognise important organelles at Class 8 level
Last-Minute Chapter Map
Plant and animal cells share basic structures but differ in cell wall, chloroplasts and typical vacuole size.
1. Cell — Basic Unit of Life
All organisms are made of cells. A cell is the smallest structural and functional unit capable of carrying out basic life processes. Amoeba is unicellular, while humans and plants are multicellular.
2. Discovery and Observation
Robert Hooke observed thin cork slices in 1665 and saw tiny box-like compartments, which he called cells. Modern microscopes reveal living cells and many internal structures that Hooke could not see.
3. Cell Shape and Size
Cells differ according to function. Nerve cells have long extensions for communication, red blood cells are shaped for transport, and muscle cells are elongated for contraction. Cell size does not simply depend on body size.
4. Cell Membrane, Cytoplasm and Nucleus
The cell membrane forms the cell boundary and regulates movement of substances. Cytoplasm is the jelly-like region where many cell activities occur. The nucleus controls many activities and contains hereditary material.
5. Plant Cell Structures
Plant cells have a rigid cell wall outside the membrane. Many plant cells contain chloroplasts for photosynthesis and a large vacuole containing cell sap. These features help distinguish typical plant cells from animal cells.
6. Organelles
Important organelles include mitochondria, which help release energy during respiration, and vacuoles, which store materials. Chloroplasts are present in photosynthetic plant cells. Class 8 study focuses on recognising their basic functions rather than detailed biochemistry.
7. Chromosomes and Genes
Inside the nucleus, genetic material is organised into chromosomes. Chromosomes carry genes, which are units of hereditary information influencing traits. Genes pass information from parents to offspring.
Plant Cell vs Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present | Absent |
| Chloroplasts | Present in green cells | Absent |
| Vacuole | Usually one large central vacuole | Usually smaller vacuoles |
| Cell membrane | Present | Present |
| Nucleus | Present in typical living cells | Present in typical cells |
Exam Focus
Must Revise Before the Exam
- Cell definition
- Hooke
- Unicellular vs multicellular
- Cell shape and function
- Cell membrane, cytoplasm, nucleus
- Cell wall, vacuole, chloroplast
- Mitochondria
- Chromosomes and genes
- Plant vs animal cell
Common Mistakes
Key Terms
Key Terms
Quick Revision
Quick Revision
- Cell = basic structural and functional unit of life.
- Hooke named cells after observing cork.
- Cell shape relates to function.
- Cell membrane regulates exchange; cytoplasm hosts many reactions; nucleus contains genetic material.
- Plant cells have a cell wall and often chloroplasts and a large vacuole.
- Mitochondria release usable energy during respiration.
- Chromosomes carry genes.
Practice Questions
Who coined the term cell after observing cork?
A. Darwin
B. Robert Hooke
C. Newton
D. Pasteur
View Solution
Correct Answer: B. Robert Hooke
Robert Hooke described cork compartments as cells.
Which structure is present in plant cells but absent in animal cells?
A. cell membrane
B. cytoplasm
C. cell wall
D. nucleus
View Solution
Correct Answer: C. cell wall
Plant cells have an outer cell wall.
Which organelle is associated with photosynthesis?
A. chloroplast
B. mitochondrion only
C. nucleus only
D. rib cage
View Solution
Correct Answer: A. chloroplast
Chloroplasts contain chlorophyll and carry out photosynthesis.
Genes are located on:
A. chromosomes
B. cell walls
C. stomata
D. vacuoles only
View Solution
Correct Answer: A. chromosomes
Genes are units of hereditary information carried on chromosomes.
Why do cells have different shapes?
View Solution
Cell shape is related to function. Nerve cells have long extensions for signalling, while muscle cells are elongated for contraction.
Differentiate cell wall and cell membrane.
View Solution
The cell membrane is a selectively controlling boundary present in cells; the cell wall is a rigid outer layer present in plant cells outside the membrane.
Why does a leaf cell commonly contain chloroplasts while a root cell deep underground may not?
View Solution
Leaf cells receive light and perform photosynthesis, so chloroplasts are useful. Underground root cells usually do not receive enough light for photosynthesis.
Chapter Summary
Chapter Summary
- Cell = basic structural and functional unit of life.
- Hooke named cells after observing cork.
- Cell shape relates to function.
- Cell membrane regulates exchange; cytoplasm hosts many reactions; nucleus contains genetic material.
- Plant cells have a cell wall and often chloroplasts and a large vacuole.
- Mitochondria release usable energy during respiration.
- Chromosomes carry genes.