Module 2 Cells

layer that surrounds the cell):
holds the contents of the cell

in place
controls what passes in and out of the cell.

A nucleus (a round structure that controls the cell):
contains chromosomes
chromosomes contain genes
genes are made of DNA
genes control features such as eye colour and ability to form finger nails
genes are passed on from parents to offspring.

Cytoplasm (a liquid that surrounds the nucleus):
carries out some cell reactions
contains small structures such as mitochondria (for energy).

structure that surrounds the cell membrane):
made of cellulose
gives strength to

the plant cell.

A cell membrane (a thin layer that surrounds the cell):
holds the contents of the cell in place
controls what passes in and out of the cell.

A nucleus (a round structure that controls the cell)
contains chromosomes
chromosomes contain genes
genes are made of DNA
genes control features such as petal colour and the shape of the leaves
genes are passed on from parents to offspring.

the nucleus):
carries out some cell reactions
contains small structures such as

chloroplasts (for photosynthesis).

Vacuole (a small liquid-filled bag in the cytoplasm):
gives strength to plant cells.

organism.

Organisms are organised into:
Cells→Tissues→Organs→Systems
MODULE 2 CELLS AND THE MICROSCOPE

the inside of your cheek with a cotton wool bud

(or wooden spatula).
Smear the saliva from the bud or spatula onto the centre of a microscope slide.
Add a few drops of methylene blue (to stain the cell).
Lower a cover slip slowly over the saliva from a 450 angle.
Soak up any unwanted stain using tissue paper.

on the light on the microscope (or adjust the mirror

so the light is shining up through the opening in the microscope stage).
Turn the nose piece so that the lowest power lens is in position.
Place the slide on the centre of the microscope stage.
Using the coarse focus knob bring the stage up as close to the objective lens as possible.
Look into the eyepiece and adjust the coarse focus knob so that the cells are clearly visible.
If necessary move the slide slightly so you can see a good sample of cells.
Draw the cells that you see at low power.
Move the high power lens into position.
Use the fine focus knob to view a clear image of cells at high power.
Draw the cell or cells at high power.

there is light passing through the opening in the stage.
Use

the lowest power lens on the nosepiece.
Clip the slide onto the stage.
Turn the coarse focus knob to bring the stage close to the slide.

MODULE 2 CELLS AND THE MICROSCOPE

from the slide.
Move the slide so that the cells of

interest are in the centre.
Adjust the amount of light passing through the slide.
Change the objective lens to a higher power and re-focus using the fine focus knob.
Draw labelled diagrams of the cells at each magnification.

MODULE 2 CELLS AND THE MICROSCOPE

onion and remove a thin layer of cells.
Place the onion

cells in water on a microscope slide.
Place a cover slip
over the onion cells.

MODULE 2 CELLS AND THE MICROSCOPE

using absorbent paper.
MODULE 2 CELLS AND THE MICROSCOPE

and more primitive than eukaryotic cells
Are found as bacteria.
A prokaryotic

cell (TEM): note the absence of a membrane around
the red chromosomes in this bacterial cell

more advanced than prokaryotic cells
Are found as plant and animal

cells, fungi and Amoeba.

A eukaryotic cell (TEM): a plant cell
showing the pink nucleus surrounded by a double membrane; the nucleolus is brown

in cells

where x = y
Types: (i) monosaccharides (one sugar unit), e.g.

glucose, fructose; (ii) disaccharides (two sugar units), e.g. sucrose, maltose; (iii) polysaccharides (many sugar units), e.g. starch, cellulose, glycogen
Sources: bread, potato, rice, flour and sweets
Structural role: cellulose forms cell walls
Metabolic role: (i) glucose is made in photosynthesis; (ii) glucose releases energy in respiration
Test: (i) reducing sugars – Benedict’s or Fehling’s solution; (ii) starch – iodine.

are liquid at room temperature
Structure: glycerol and three fatty acids

= triglyceride
Sources: butter, cream, oils and fried food
Structural role: (i) store energy; (ii) insulate; (iii) form membranes
Metabolic role: release energy in respiration
Test: brown paper.

Structure of a lipid (triglyceride)

peptides, polypeptides and protein
Sources: meat, fish, eggs and milk
Structural role:

form structures such as skin, hair, nails and muscle
Metabolic role: (i) enzymes;
(ii) some hormones;
(iii) antibodies
Test: sodium hydroxide, then copper sulfate (the Biuret test).

Keratin: a protein found in hair and nails

Foods rich in protein