Cell theory, cell organelles, and how plant and animal cells differ.
A quick tour inside plant and animal cells. Video coming soon.
↔ Swipe the diagram sideways to see all of it
Robert Hooke (1665) saw box-like compartments in cork and named them cells. Schleiden and Schwann (1838–39) proposed that all living things are made of cells; Virchow (1855) added that new cells arise only from existing cells. Cells may be prokaryotic (no true nucleus, e.g. bacteria) or eukaryotic (true nucleus with a nuclear membrane).
State the cell theory in three points.
All living things are made of cells. The cell is the basic unit of structure and function. New cells come only from pre-existing cells.
Distinguish prokaryotic from eukaryotic cells.
Prokaryotic: no nuclear membrane, no membrane-bound organelles, e.g. bacteria. Eukaryotic: a true nucleus with a membrane and many organelles, e.g. plant and animal cells.
A red blood cell is 7 µm across. A student draws it 3.5 cm wide. Find the magnification.
3.5 cm = 35000 µm. Magnification = drawing size ÷ actual size = 35000 ÷ 7 = 5000×.
A microscope has a 10× eyepiece and a 40× objective. Total magnification?
10 × 40 = 400×.
Cell wall (cellulose, plants only): shape and protection. Plasma membrane: selectively permeable. Cytoplasm: jelly where reactions occur. Nucleus: controls the cell and holds chromatin (DNA). Mitochondria: release energy in respiration. Endoplasmic reticulum: transport and, with ribosomes, protein making. Ribosomes: make proteins. Golgi bodies: package and secrete. Lysosomes: digest waste and worn-out parts. Plastids: chloroplasts photosynthesise. Vacuoles: store water and substances. Centrosome (animal cells): cell division.
Which organelle is called the "powerhouse of the cell"? Why?
Mitochondrion, because it releases the energy from food in respiration.
Which organelle is called the "suicide bag"?
Lysosome. If the cell is damaged its enzymes digest the cell itself.
Name the pigment in chloroplasts and its function.
Chlorophyll; it traps light energy for photosynthesis.
Both have a plasma membrane, cytoplasm, nucleus, mitochondria, ER, ribosomes and Golgi bodies. Plant cells also have a cell wall, chloroplasts and a large central vacuole. Animal cells have a centrosome and only small vacuoles.
Give three differences between a plant cell and an animal cell.
Plant: cell wall present, chloroplasts present, large central vacuole. Animal: no cell wall, no chloroplasts, small vacuoles; centrosome present.
Why do plant cells keep a fixed shape while animal cells can change shape?
The rigid cell wall of cellulose holds the plant cell in shape. Animal cells have only a flexible membrane.
1. Who named the cell and in what material did he see it?
2. What did Virchow add to the cell theory?
3. Name one prokaryote and one eukaryote.
4. What is the function of the cell membrane?
5. Where are proteins made in the cell?
6. What are plastids? Name the three types.
7. Name an organelle found in animal cells but not in plant cells.
8. A cell is 8 µm wide and is drawn 2.4 cm wide. Find the magnification.
9. Name the part of the nucleus that carries hereditary information.
10. Why is the cell called the "unit of life"?