Cell structure
AdvancedA cell contains structures with different jobs; plant cells have a cell wall, chloroplasts and a large vacuole that animal cells lack.
- Both cells: membrane, cytoplasm, nucleus, mitochondria
- Plant-only: cell wall, chloroplast, large vacuole
- Nucleus = control centre; membrane = gate; mitochondria = powerhouse
§Text Passage
1Magnified, a cell looks like a tiny factory working with great precision. Animal and plant cells both contain a cell membrane, cytoplasm and a nucleus. The membrane surrounds the cell and controls what enters and leaves; the cytoplasm is where many chemical reactions take place; the nucleus stores genetic material and, like a control centre, directs the cell's activities.
2Plant cells have three extra structures that animal cells lack. The cell wall is the rigid outermost layer that keeps the cell in a fixed shape; chloroplasts contain chlorophyll and capture sunlight to make food; the large vacuole stores water and nutrients, keeping the cell firm and upright. These three are the main evidence for telling the two kinds of cells apart.
3These structures connect closely to everyday life. The crunch when you bite raw celery comes from rigid cell walls and water-filled vacuoles, while the green colour and food-making of a leaf depend on chloroplasts. Onion skin lies buried underground where sunlight never reaches, so its cells contain almost no chloroplasts, yet they are still plant cells.
4Each structure has its own job, showing how structure and function work hand in hand. Mitochondria, found in both animal and plant cells, break down nutrients to release energy, while chloroplasts convert light energy into stored chemical energy. Understanding this division of labour helps explain photosynthesis and heredity, and even guides scientists in developing antibiotics that target bacterial structures.
1Summary 重點摘要
A cell contains structures with different jobs; plant cells have a cell wall, chloroplasts and a large vacuole that animal cells lack.
2Vocabulary cards Vocabulary
The control centre of the cell.
Controls what enters and leaves the cell.
Jelly-like substance where reactions happen.
Plant cells only: rigid outer layer for support.
Plant cells only: where photosynthesis happens.
Stores water and substances; large in plant cells.
The powerhouse: releases energy for the cell.
The instructions stored in the nucleus that determine an organism's traits and are passed to the next generation.
3Step by step Steps
- Found in bothAnimal and plant cells share four basic structures: the cell membrane, cytoplasm, nucleus and mitochondria. The membrane encloses the cell and controls what enters and leaves; the cytoplasm is where many chemical reactions take place; the nucleus stores genetic material and directs the cell's activities; and mitochondria break down nutrients to release energy. These four are the basis of cell life — lacking any one of them, a cell could hardly work properly.
- Plant cells onlyPlant cells have three extra structures: a cell wall, chloroplasts and a large vacuole. The cell wall is the rigid outermost layer that supports and protects the cell; chloroplasts contain chlorophyll and are the site of photosynthesis; the large vacuole stores water and dissolved substances, keeping the cell firm and upright. These three are present in plant cells but absent from animal cells — the main difference between the two and a favourite point for exam comparison.
- Remember the jobsTo remember what each structure does, think of their jobs: the nucleus is the command centre giving orders, the membrane is the security guard watching the gates, the mitochondria are the power station supplying energy, and the chloroplast is the kitchen making food. Recall the job first and the name follows, so nothing gets left out. The crunch when you bite raw celery comes from its rigid cell walls — linking knowledge to daily life makes it stick.
- How to judgeTo classify a cell, rely on its marker structures: the presence of a cell wall proves a plant cell, since animal cells have none. Chloroplasts need more care, because they gather only in light-exposed green parts; onion skin grows underground and hardly ever sees light, so it has almost no chloroplasts yet is still a plant cell. Never mistake such a cell for an animal cell just because chloroplasts are missing.
- Compare under the microscopeIn practical lessons you can compare the two cells yourself: onion-skin cells have a cell wall and tile neatly like bricks, while cheek-lining cells have no wall and look rounder, their nuclei standing out clearly after methylene-blue staining. Afterwards, draw exactly what you see, label every structure and note the magnification, so that others can repeat and check the observation — that is what separates a scientific record from a casual sketch.
- Two energy structuresMitochondria and chloroplasts are the easiest pair to confuse, so separate them by the direction of their work: mitochondria occur in both animal and plant cells, breaking nutrients down to release energy — the powerhouse of every cell; chloroplasts exist only in the lit parts of plants, converting light energy into chemical energy stored in glucose. One releases energy and the other stores it, and together they keep energy flowing through the living world.
4Diagrams Diagrams
5Worked example Example
Example: onion skin cells have a cell wall but no chloroplasts. Why are they still plant cells?
- Plant cells always have: cell wall, membrane, cytoplasm, nucleus
- Chloroplasts appear in parts exposed to light
- Onion skin grows underground — few chloroplasts
- The key marker is the cell wall, not the chloroplasts
- Answer: Because onion-skin cells have a cell wall — the hallmark of plant cells, which animal cells lack. Chloroplasts gather in light-exposed green parts, while onion skin grows underground and rarely sees light, so it has very few. The key test is the cell wall, not the number of chloroplasts — that is the safe way to judge.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which structure is the control centre of the cell?
Q2Name one structure found in plant cells but not animal cells.
Q3What do mitochondria do?
Q4Which structure gives raw celery its crunchy bite?
Q5What is the function of the cell membrane?
8Recap Recap
- Both cells: membrane, cytoplasm, nucleus, mitochondria
- Plant-only: cell wall, chloroplast, large vacuole
- Nucleus = control centre; membrane = gate; mitochondria = powerhouse
- Structure matches function — the cell wall supports plant cells
- Onion skin cells lack chloroplasts because they are buried away from sunlight