practice errors made (component three)

Question 1

explain what is meant by homeostasis

Answer 1

it is the maintenance of a constant internal environment in the body, to counteract a stimulus and provide the optimal condition for reactions in the body

Question 2

why does a person not feel thirsty after an increase in the solute potential of the blood but only after a certain threshold

Answer 2

Because, straight after the solute potential increases, the ADH released into the bloodstream by the posterior pituitary gland can achieve sufficient water reabsorption through the collecting ducts

after reaching a certain threshold, the solute potential becomes too high and the person has to drink water to avoid dehydration, hence they become thirsty.

Question 3

name three conditions that stimulate to ADH secretion

Answer 3

severe diarrhea
vomiting
blood loss

Question 4

explain how the nephron and it’s blood supply are adapted for ultrafiltration

Answer 4

the glomerulus has a high hydrostatic blood pressure which forces small molecules like glucose out of the capillaries

the capillaries have fenestrae through which the molecules leave into the PCT

podocytes and pedicels in the basement membrane increase the filtration rate

the basement membrane is permeable to water and glucose but not large molecules like protein and starch

the efferent arteriole is narrower that the afferent arteriole and that increases the pressure in the glomerulus

Question 5

explain how chloride ions are selectively reabsorbed

Answer 5

they diffuse through the phospholipid membrane of the cells of the PCT by facilitated diffusion, through channel proteins, down their concentration gradient

Question 6

explain how water is selectively reabsorbed

Answer 6

water moves through the partially permeable membranes of the cells of the PCT by osmosis, down it’s water potential gradient

Question 7

explain how sodium ions are selectively reabsorbed

Answer 7

they have actively transported out the cells of the PCT, using energy from ATP against their concentration gradient, through a sodium-potassium pump.

there are more sodium ions in the filtrate than in the PCT cells, so a concentration gradient is generated

the sodium ions diffuse down their concentration gradient into the PCT cells, through channel proteins, which only allow the sodium ions to diffuse through if coupled with glucose

Question 8

a parasite

Answer 8

an organism that lives in a host and obtains nourishment at the expense of the host, by doing harm to it

Question 9

autotroph

Answer 9

organism that uses inorganic molecules to synthesise organic compounds

Question 10

saprobionts

Answer 10

organisms that secrete enzymes on food outside the body, thereby feeding by extracellular digestion, and then absorbing the products by diffusion

Question 11

three features of the gut parasite that are characteristics to their parasitic way of life

Answer 11

they produce a large number of eggs
they have hooks and suckers for attachment to the host’s gut
they are thin, to provide a large surface area for absorbing pre-digested food by the host
they have no digestive system, as they feed on pre-digested food by the host

Question 12

how is the mode of nutrition of parasites similar to that of carnivores

Answer 12

they both feed by doing harm to other organisms

Question 13

how is the parasitic mode of nutrition different from that of a carnivore

Answer 13

carnivores digest their own diet, while parasites feed on a pre-digested diet by their host

carnivores have a digestive system while parasites do not

parasites absorb food externally, while carnivores absorb food internally

Question 14

how is a tapeworm adapted to resist peristalsis in the human intestine

Answer 14

it has hooks and suckers to attach to the intestinal walls

Question 15

why does a tapeworm not need a mouth for feeding

Answer 15

because it absorbs it’s nutrients through it’s body surface, so there is no need for a mouth

Question 16

functions of cuticles on the body of a tapeworm

Answer 16

it protects the worm from the effects of enzymes and acids in the gut

Question 17

functions of muscles in the body wall of tapeworms

Answer 17

it allows the tapeworm to increase contact with the digested food

Question 18

how does a low-protein diet lead to fluid retention in the tissues

Answer 18

presence of proteins reduces water potential of the blood

so less protein means a higher water potential of the blood

so there is little water potential gradient between the blood and the fluid

so less water is reabsorbed into the blood(more water remains in the tissue fluid)

Question 19

why are log scales used on the axes of graphs

Answer 19

it makes it easy to compare values that cover a large range

Question 20

apart from the exchange of gases and nutrients, state three other roles of the placenta

Answer 20

provides a barrier between the maternal and foetal blood

protects the foetus from the mother’s immune system

protects the foetus from differences between the mother’s and the foetal’s blood

Question 21

advantage of a 25 percent increase of red blood cells in the blood of a pregnant woman

Answer 21

can carry more oxygen to the developing foetus

Question 22

advantage of a parasite not secreting digestive enzymes

Answer 22

does not have to waste it’s own resources in synthesizing it’s own digestive system

Question 23

advantages of capillaries being narrow

Answer 23

friction in blood vessel increases, so blood flow is slower

therefore there is more time for exchange of substances to occur

Question 24

features of water that enable it to travel up the xylem

Answer 24

hydrogen bonds formed between partially positive hydrogens and partially negative oxygen of adjacent water molecules provide cohesion

this creates a transpiration stream up the xylem as water leaves the leaves during transpiration

Adhesion is also provided to the walls of the xylem vessel

Question 25

describe how guard cells open to allow the stomata to open

Answer 25

potassium ions move into the guard cells by active transport

starch is converted to malate, thereby further lowering the water potential of the guard cells

water flows into the guard cells down the water potential gradient by osmosis

turgor increases, and the guard cells curve away from each other, opening the stomata

Question 26

why do guard cells curve away from each other as water moves into them

Answer 26

the inner wall is thicker and inelastic compared to the outer wall

Question 27

Cadmium is thought to affect enzymes involved in the LDR of photosynthesis. Palisade mesophyll cells taken from a plant grown in high concentrations of cadmium were found to contain more TP than normal. Using your knowledge of the Calvin cycle, explain this observation

Answer 27

Cadmium inhibits activity of the enzyme that converts TP to the next product in the Calvin cycle

SO TP concentration increases, as it cannot be converted

Question 28

why do starch grains appear blue under a microscope

Answer 28

they are stained with iodine, which turns blue-black in the presence of starch

Question 29

how does the ribcage moving upwards and outwards increase the volume in the pleural cavity

Answer 29

causes the inner pleural membrane to move outwards

pulls on the surface of the lungs and causes the alveoli to expand, thereby increasing the volume

Question 30

suggest why the presence of Hydrogen ions in the small intestines might decrease the rate of absorption of assimilates into the blood stream

Answer 30

reduces PH
which could denature enzymes to catalyze the rate of absorption
so fewer assimilates are absorbed

it could also denature the active site of carrier proteins of cells in the intestinal walls
so assimilates will not fit, as they will not be complementary in shape to the active site
so the intestinal walls become impermeable to the assimilates, and fewer assimilates are absorbed

Question 31

guidelines to follow when drawing diagrams in biology

Answer 31

do not use sketch lines
add a magnification bar
show tissue layers not individual cells
no shading in diagram

Question 32

People that carry an infection but do not develop symptoms are referred to as

Answer 32

Asymptomatic carriers

Question 33

how viruses cause pathogenic effects

Answer 33

through cell lysis

by suppressing the host organism’s immune system

by triggering the host cells to become cancerous

Question 34

why was the smallpox vaccination a success

Answer 34

there was a low rate of mutation and so little antigenic variation took place

there is no animal reservoir of the virus

there was a simple vaccination program in which the vaccination was easy to give and people were keen to be immunised

Question 35

why might vaccines for some pathogens not be 100% effective

Answer 35

due to the emergence of new strains by mutations