IGCSE review guide

Question 1

What are the characteristics of living organisms? Describe them.

Answer 1

Order: organisms are highly organized, coordinated structures that consist of one or more cells.

Sensitivity: organisms respond to diverse stimuli.

Reproduction: single-celled organisms reproduce by first replicating their DNA, and dividing it equally as the cell prepares to decide to form two new cells.

Development: organisms grow and develop following specific instructions coded for by their genes.

Homeostasis: Steady level of internal, physical, and chemical conditions maintained by the control system.
Energy processing: all organisms use a source of energy for their metabolic activities.

Question 2

Describe the differences in structure between typical animal and plant cells, explaining the function of each organelle.

Answer 2

Animal cell:
Nucleus: contains DNA controls cell activity.
Cell membrane: a flexible layer that surrounds the cell.
Mitochondria: energy is released from food molecules.

Plant cells:
Cell wall: hard layer outside the cell, provides strength to the plant.
Vacuole: store substance, helps cells keep their shape.
Chloroplasts: contain green pigment (chlorophyll), the key to photosynthesis.

Differences:
Plants cells have a cell wall, while animal cells do not… plant cells have chloroplasts, animal cells do not. Plant cells have a large vacuole, where usually animal cells do not have.

Question 3

How can magnification of biological specimens be calculated? Give an example to illustrate your answer.

Answer 3

Magnification is the process of enlarging the apparent size, not the physical size of something. 
Measure scale bar image in (mm)
Convert to micrometers (x1000)
Magnification = scale bar image ÷ actual space bar
Formulas: 
Size of image ÷ actual size of object 
Size of image ÷ magnification
Actual size of object x magnification

Question 4

What is diffusion?

Answer 4

Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration. Diffusion occurs in liquid and gasses when their particles collide randomly and spread out. Diffusion is an important process for living things, as it is new substances moving in and out of cells.

Question 5

What is the importance of diffusion of gasses and water (osmosis) for the survival of organisms? Give examples to illustrate your answer.

Answer 5

Diffusion is important to cells because it allows them to gain the useful substance they require to obtain energy and grow and lets them get rid of waste products.

Substance required by cell:
Glucose
Oxygen
Amino acids

Waste product by cell:
Carbon dioxide
urea