Biology Notes
- Unit 3
3.1
The Discovery of Cell
(a) A living organism composed of one or many cells.
(b) The basic unit of structure and function in living organisms.
(c) First used by Robert Hooke, a British scientist.
3.2
The Structure of a Typical PLANT Cell
Cell wall
Non-living granule
Cell membrane
Chloroplast
Cytoplasm
Mitochondrion
(A)
Vacuole
Cell wall
(1) Found in plant cells only
(2) Made of cellulose which forms very thin fibers
(3) Cellulose fibers cross over one other to form a very strong
covering to the cell
★ Function
(a) To protect and support the enclosed protoplasm
(b) To resists entry of excess water into the cell
(4) Large molecules can penetrate the cell wall
∵large space between the cellulose fibers
Middle lamella is lying between the cell walls of 2 adjacent
plant cells
Thin layer of pectin substance which join neighboring cells
together
Pages 1/5
(B) Protoplasm
(1) Cell membrane
(a) All cells are surrounded by a cell membrane.
(b) Very thin
★(c) A selectively permeable layer, controlling the movement
of materials into and out of all
(2) *Cytoplasm
(a) A clear, jelly-like substance enclosed by the cell membrane
(b) Consists of an aqueous solution of many substances
E.g. Protein
(c) Contains a variety of organelles and non-living granules
(α) Chloroplasts
~ Large bodies in green plant cells
~ Contain the green pigment chlorophyll used in
photosynthesis
~ Contain starch grains which are products of
photosynthesis
(β) Mitochondria / Mitochondrion
~ Respiration occurs inside it
~ Sometimes call the ‘powerhouse’ of the cell
~ Active cells
E.g. Sperm, have more mitochondria than inactive ones.
(γ) Non-living granules
~ E.g. Crystals of insoluble waste and starch granules
(C) Vacuole
(a) Fluid-filled space in a cell surrounded by a membrane called
tonoplast
(b) Contains a solution of sugar, proteins and mineral-salts called
cell sap
*Cytoplasm 細胞質
Pages 2/5
(D) Nucleus / Nucler
(a) Generally spherical
(b) Functions: controls the normal activities of the cell
(c) Stores genes which help the ribosomes to make the right kinds
of proteins
(d) The genes are made of DNA (Deoxyribonucleic Acid) and are
located on the chromosomes
(e) Chromosome are visible only in a dividing cell
(f) They appear as chromatin in a non diving cell
(g)They appear as chromatin in a nuclear membrane which has tiny
pores and is selectively permeable
3.21 Summary of the Structure of a Typical PLANT Cell
Plant Cell
Cell Wall
Cell membrane
Protoplasm
Cytoplasm
Vacuole
1. Chloroplasts
2. Mitochondria
3. Non-living granules
Nucleus
1. Nuclear membrane
2. Chromatins
Pages 3/5
3.3
The Structure of a Typical ANIMAL Cell
1> No cell wall or chloroplast
2> Made of protoplasm enclosed by the cell membrane
3> The vacuoles are small and exist temporarily
4> Store glycogen (肝糖) and oil droplets in the cytoplasm
5> Greater variety of forms and functions among animals than that
among plant cells
Cell membrane
Mitochondrion
Vacuole
Cytoplasm
Nuclear membrane
Granules
Nucleus
Chromatin
3.31 Summary of the Structure of a Typical ANIMAL Cell
Animal cell-protoplasm
Cytoplasm
1. Mitochondria
2. Non-living granules
of glycogen and oil
Cell membrane
Nucleus
1. Nucleus membrane
2. Nucleolus
3. Chromatins
Pages 4/5
3.4
Comparison between Plant Cells & Animal Cells
Similarities:
1> Both have a cell membrane (surrounding the cytoplasm)
2> Both have a nucleus
3> Both contain mitochondria
Differences:
1> Size & Shape
2> Cell Wall
3> Chloroplasts
4> Vocuoles
Plant Cells
Animal Cells
Large and Regular
Smaller and Irregular
With a cellulose cell wall
Without cell wall


With chloroplasts
containing chlorophyll
Without chloroplasts


With large vacuoles
(containing cell sap)
Vacuoles small or absent
(containing secretory 分泌
or excretory products)
5> Food Reserves
Starch granules
Glycogen granules (oil)
6> Site of Nucleus
Nucleus usually found
Nucleus usually found in
just beneath the cell
wall
the cell centre
Pages 5/5