Cell Structure: Notes and Sample Answers

Microscopes:

  • Simple microscopes have 1 lens.
  • Compound microscopes have 2 lenses.
  • Electron microscopes show cell ultrastructure.
->Transmission electron microscope shows internal structures.
->Scanning electron microscopes shows surfaces.

Ultrastructure of a generalised cell:


The protoplasm is all living parts of the cell.

Cytoplasm:
  • Living material outside the nucleus.
  • Contains cell organelles (Small bodies that carry out functions like mitochondria, ribosomes)
  • Cytosol is the jelly like substance minus the cell organelles.

Plasma (cell) membrane:
  • Surrounds the cell.
  • Made up of phosolipids (which forms a phosolipid bilayer) & proteins.
  • Function is to control the entry & exit of molecules from the cell (semi permeable) and to retain cell contents.

Nuclear pores:
  • Allow mRNA to pass in and out of the nucleus.

Nucleus:
  • Function is to control the cell.
  • Contains chromosomes made of DNA.
  • Elongated, non dividing chromosomes are called chromatin.

DNA:
  • Stands for deoxyribonucleic acid.
  • Found in chromosomes/chromatin in the nucleus.

Nucleolus:
  • Found in the nucleus.
  • Makes ribosomes.

Mitochondrion:
  • Function is to provide energy ( sites of respiration)
  • Numerous in active cells (muscle).
  • Many infoldings imply large energy output.

Ribosomes:
  • Make proteins.
  • Made of RNA & protein.

Cell wall:
  • Plants only.
  • Made of cellulose.
  • Function is strength & support.
  • Fully permeable.

Vacuoles: 
  • Found mainly in plants.
  • Functions are to strengthen the cell & storage.

Chloroplasts:
  • Found only in plants.
  • Carry out photosynthesis.
  • Contain green pigment called chlorophyll.


Biology HL paper 2011:

Question 14 (C)
(i) State the precise location of the cell membrane in plant cells.
Immediately inside the cell wall.
(ii) With what type of cell do you associate membrane-bound organelles? 
Eukaryotic.
(iii) What corresponding term is used to describe bacterial cells? 
Prokaryotes.
(iv) The cell membrane is described as being selectively permeable. What does this mean? 
This is where the membranes can allow the passage of some molecules and prevent the passage of others. 

Biology HL paper 2006:
Question 8 
(a)State a function of each of the following components of a cell. 
(i) Ribosome:  This is the part that makes proteins.
(ii) Cell membrane: Retains the contents of the cell and allows certain molecules to pass in and out of the cell. 

(b) Answer the following questions in relation to the preparation, staining and microscopic observation of a slide of an animal cell. 
(i) What type of animal cell did you use? A cheek cell. 
How did you obtain the cell? After rinsing my mouth with water, I swabbed the inside of my cheek with a cotton swab in order to collect cells.

(ii) Name the stain that you used: Methylene blue
Describe how you applied the stain: I spread some of the cells onto a glass slide using the cotton swap. I used a dropper to drop some of the methylene blue onto the cells in order to stain them a deep blue colour.

(iii) After staining, a cover slip is placed on the slide. Give a reason for this
This is done to eliminate air bubbles, to prevent the cells from drying out and to prevent the lens from getting wet.

(iv) How did you apply the cover slip?
I applied the cover slip carefully at an angle, this is done in order to eliminate any air bubbles. 
Why did you apply it in this way?
In order to eliminate air bubbles. 

(v) Describe the difference in colour or depth of colour, if any, between the nucleus and cytoplasm when the stained cell was viewed under the microscope. 

When viewed under the microscope, it can be seen that the nucleus & cell organelles are more stained than the cytoplasm, allowing us to see the contents of the cell more clearly.
625 points Leaving Cert Notes
Leaving Cert Sample Answers and Notes



Get Excellent Free Notes From Top Leaving Cert Performers Straight To Your Inbox

* indicates required