Pearson Edexcel IGCSE Biology Test
Questions and Answers.
Describe how substances can pass into and out of the cell surface membrane (6 marks) - Answer
Diffusion is the movement of molecules from an area of high concentration to an area of low
concentration e.g. small, non-polar molecules (oxygen and carbon dioxide)
• Facilitated diffusion is the movement of molecules from an area of high concentration to area
of low concentration and requires carrier or channel proteins. Examples are larger, polar
molecules e.g. glucose
• Active transport is the movement of molecules against a concentration gradient. Energy in the
form of ATP is required. Examples include amino acids into the epithelium of the small intestine.
• Phagocytosis- pathogen is engulfed by the white blood cells
How vaccines protect people from disease - Answer - Vaccine contains antigen from
pathogen
- Antigen presentation on cell surface membrane of B cell
- T-helper cell stimulates B cell, it activates it, with complementary receptor on its surface
(clonal expansion)
- B cell divides by mitosis to become clones (genetically identical) of B cell (clonal expansion)
which have complementary receptor on its surface to antigen
- b cells become plasma cells which produce large amounts of antibodies
- some B cells become memory cells and stay in blood and tissues
- When exposed to antigen memory cells differentiate into plasma cells quickly to quickly
produce antibodies so unlikely to suffer symptoms
When the skin is too hot - vasodilation - Answer 1. blood vessels near skin dilate via
vasodilation to increase blood flow to surface
2. sweat glands excrete sweat to cool skin via evaporative cooling
3. hair erectors muscles relax to lower skin hair, trapping a thin insulation layer of air above the
skin.
When the skin is too cold - vasoconstriction - Answer 1. blood vessels near skin contract via
vasoconstriction to reduce blood flow to surface
2. sweat glands do not excrete sweat
3. hair erectors muscles contract to raise skin hair, trapping a thick insulating layer of air above
the skin.
ADH - source, role, effects - Answer pituitary gland, osmoregulation, increasing the
permeability of the collecting duct
Questions and Answers.
Describe how substances can pass into and out of the cell surface membrane (6 marks) - Answer
Diffusion is the movement of molecules from an area of high concentration to an area of low
concentration e.g. small, non-polar molecules (oxygen and carbon dioxide)
• Facilitated diffusion is the movement of molecules from an area of high concentration to area
of low concentration and requires carrier or channel proteins. Examples are larger, polar
molecules e.g. glucose
• Active transport is the movement of molecules against a concentration gradient. Energy in the
form of ATP is required. Examples include amino acids into the epithelium of the small intestine.
• Phagocytosis- pathogen is engulfed by the white blood cells
How vaccines protect people from disease - Answer - Vaccine contains antigen from
pathogen
- Antigen presentation on cell surface membrane of B cell
- T-helper cell stimulates B cell, it activates it, with complementary receptor on its surface
(clonal expansion)
- B cell divides by mitosis to become clones (genetically identical) of B cell (clonal expansion)
which have complementary receptor on its surface to antigen
- b cells become plasma cells which produce large amounts of antibodies
- some B cells become memory cells and stay in blood and tissues
- When exposed to antigen memory cells differentiate into plasma cells quickly to quickly
produce antibodies so unlikely to suffer symptoms
When the skin is too hot - vasodilation - Answer 1. blood vessels near skin dilate via
vasodilation to increase blood flow to surface
2. sweat glands excrete sweat to cool skin via evaporative cooling
3. hair erectors muscles relax to lower skin hair, trapping a thin insulation layer of air above the
skin.
When the skin is too cold - vasoconstriction - Answer 1. blood vessels near skin contract via
vasoconstriction to reduce blood flow to surface
2. sweat glands do not excrete sweat
3. hair erectors muscles contract to raise skin hair, trapping a thick insulating layer of air above
the skin.
ADH - source, role, effects - Answer pituitary gland, osmoregulation, increasing the
permeability of the collecting duct
