(a)(i) Cell theory states that:
(1) the cell is the smallest unit of life.
(2) The cell is the unit of function of life.
(3) New cells are produced from existing cells.
(4) All living things have cells and cell products.
(ii)(1) Robert Hook
(2) M. J. Schleiden
(c) Differences between a plant and animal cell are:
| Plant cell | Animal cell |
| (1) Possesses large vacuole(2) Possesses chloroplast (3) Possesses cellulose cell wall | - Has small vacuole- Has no chloroplast- Has no cellulose cell wall. |
(d) Difference between Hydra and mammal:(i)
Level of organization: Hydra is organised in the tissue level while mammal is organised in the system level
(ii)
Symmetry: Hydra is radially symmetrical while mammal possesses bilateral symmetry
(iii) Hydra possesses two body layers, e.g. ectoderm and endoderm while mammal possesses three layers.
