Animal cages. Plant cells

1.

Module 2
Cells

2.

Animal cells have the following parts
A cell membrane (a thin layer that surrounds the cell):
o holds the contents of the cell in place
o controls what passes in and out of the cell.
A nucleus (a round structure that controls the cell):
o contains chromosomes
o chromosomes contain genes
o genes are made of DNA
o genes control features such as eye colour and ability to form
finger nails
o genes are passed on from parents to offspring.
Cytoplasm (a liquid that surrounds the nucleus):
o carries out some cell reactions
o contains small structures such as mitochondria (for energy).

3.

Animal cells have the following parts

4.

Plant cells have the following parts
A cell wall (a strong structure that surrounds the cell membrane):
o made of cellulose
o gives strength to the plant cell.
A cell membrane (a thin layer that surrounds the cell):
o holds the contents of the cell in place
o controls what passes in and out of the cell.
A nucleus (a round structure that controls the cell)
o contains chromosomes
o chromosomes contain genes
o genes are made of DNA
o genes control features such as petal colour and the shape of the
leaves
o genes are passed on from parents to offspring.

5.

Plant cells have the following parts
Cytoplasm (a liquid that surrounds the nucleus):
o carries out some cell reactions
o contains small structures such as chloroplasts (for
photosynthesis).
Vacuole (a small liquid-filled bag in the cytoplasm):
o gives strength to plant cells.

6. MODULE 2 CELLS AND THE MICROSCOPE

• Cell division is the basis for the growth of an organism.
• Organisms are organised into:
Cells→Tissues→Organs→Systems

7.

Activity 2.1: How can we examine animal cells
Prepare the slide
1.Scrape the inside of your cheek with a cotton wool bud (or wooden
spatula).
2.Smear the saliva from the bud or spatula onto the centre of a microscope
slide.
3.Add a few drops of methylene blue (to stain the cell).
4.Lower a cover slip slowly over the saliva from a 450 angle.
5.Soak up any unwanted stain using tissue paper.

8.

Activity 2.1: How can we examine animal cells
Viewing the slide
1.Turn on the light on the microscope (or adjust the mirror so the light is
shining up through the opening in the microscope stage).
2.Turn the nose piece so that the lowest power lens is in position.
3.Place the slide on the centre of the microscope stage.
4.Using the coarse focus knob bring the stage up as close to the objective
lens as possible.
5.Look into the eyepiece and adjust the coarse focus knob so that the cells
are clearly visible.
6.If necessary move the slide slightly so you can see a good sample of
cells.
7.Draw the cells that you see at low power.
8.Move the high power lens into position.
9.Use the fine focus knob to view a clear image of cells at high power.
10.Draw the cell or cells at high power.

9. MODULE 2 CELLS AND THE MICROSCOPE

• To examine animal or plant cells under a microscope:
– Make sure 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.

10. MODULE 2 CELLS AND THE MICROSCOPE

– Turn the coarse focus knob to bring the lens away 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.

11. MODULE 2 CELLS AND THE MICROSCOPE

• Activity 2.3
• To prepare a slide from plant
tissue:
–Cut an 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.

12. MODULE 2 CELLS AND THE MICROSCOPE

• Draw a few drops of iodine solution across the cells using
absorbent paper.

13.

Prokaryotic cells:
•Do not have a nucleus or membrane-enclosed organelles
•Are small 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

14.

Eukaryotic cells:
•Have a membrane-enclosed
nucleus and cell organelles
•Are larger and 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

15. Substances in cells

The main substances found in cells are:
•Lipids
•Carbohydrates
•Nucleic acids
•Proteins

16. Substances in cells

The main substances cells need to survive are:
• Carbohydrates
• Lipids
• Nucleic acids
• Proteins

17.

Carbohydrates:
•Made of C, H and O in the ratio Cx(H2O)y, 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.

18.

Lipids:
•Made of C, H and O
•Fats are solid and oils 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)

19.

Proteins:
•Made of C, H, O, N, (S, P)
•Structure: amino acids, 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).
Foods rich in protein
Keratin: a protein found in hair and nails