past paper questions mistakes

Question 1

explain how an increase in temperature would affect results of pondweed photosynthesis invesitagtion

Answer 1

bubbles (of gas) would be
produced faster
(because) enzymes work faster

Question 2

what is photosynthesis controlled by?

Answer 2

enzymes

Question 3

two improvements to pondweed photosynthesis practical so results more valid

Answer 3

-repeat + calculate mean
-use the same bulb/lamp
-measure volume of gas produced
-allow pondweed time to equilibriate

Question 4

what does exothermic mean?

Answer 4

releases energy (to the
surroundings)
(thermal energy)

Question 5

suggest why a layer of oil was needed on the surface of the mixture(of yeast and sugar solution)

Answer 5

-to keep oxygen out
-to prevent aerobic respiration

Question 6

explain results from 0 minutes to 45 minutes for flask kept at 35 degrees
(experiment: effect of temperature on fermentation in yeast)

Answer 6

-ideal temperature for enzymes to work so co2 produced rapidly
-after time (around 15 minute) fermentation slowed
(because) sugar/glucose / food
began to run out

Question 7

explain how releasing sterile mosquitoes reduces the spread of malaria

Answer 7

reduces breeding/reproduction
(in mosquitos)
(so) fewer mosquitos to bite
people or (so) fewer mosquitos to pass on pathogen / protist

Question 8

how much is 1 µm (i micrometre ) of a metre

Answer 8

x 10 ^-6

Question 9

explain why plants infected with tobacco mosaic virus grow slowly

Answer 9

-discolouration in leaves –> less chlorophyll so reduced photosynthesis
(so) less glucose produced so
less amino acids / proteins /
cellulose made

Question 10

what is the correct order for blood flowing through the heart to the lungs?

Answer 10

right atrium → right ventricle →
pulmonary artery

Question 11

what are stem cells?

Answer 11

stem cells are undifferentiated cells

Question 12

describe how water is transported from the soil to the atmosphere through a plant

Answer 12

-water is absorbed from soil by osmosis through the root hair cells
-travels through xylem vessels which carry water up the plant by transpiration
-water lost through stomata as it evaporates

Question 13

explain one way sieve tube cells are specialised for their functions

Answer 13

• have pores in the end walls so dissolved sugars can move from cell to cell
  or
  have pores in the end walls to maximise space for the movement of dissolved sugars

Question 14

what does the structure of the companion cells suggest about the process that moves dissolved sugars through the phloem tissue?

Answer 14

(the process):
* requires energy
* is an active process
* uses active transport
(reason) cells have many
mitochondria

Question 15

describe why it is important that dissolved sugars are moved both upwards and downwards in a plant

Answer 15

sugars are made in the leaves
by photosynthesis
all cells/tissues need sugar for
respiration
(sugars) transported to
meristems for growth/cell
division/mitosis

Question 16

suggest one reason why the results must be reviewed by other scientists.

Answer 16

to prevent false claims
* to make sure the results /
conclusions are correct / valid
* to avoid bia

Question 17

describe and explain,as fully as you can, the effects of exercise on skin temperature

Answer 17

-heat produced by muscles during exercise by respiration so skin temperature over muscles rises

Question 18

the concentration of live bacteria continued to increase after starting the course of antibiotics.
suggest one reason why

Answer 18

any one from:
* only a few bacteria killed so
live bacteria continued to
reproduce
* time delay before antibiotic
reached bacteria
* time delay before antibiotic
could kill bacteria

Question 19

how many cell divisions are needed to form a 16-cell embryo from the original fertilised egg cell?

Answer 19

4

Question 20

when it asks you to compare stuff from a graph / use a graph

Answer 20

explicitly state comparisons shown in the graph / every comparison directly from figure shown

Question 21

explain how the structure of enzyme molecules is related to the effect of pH on the activity of amylase

Answer 21

enzymes are protein molecules
* (so) have a 3D structure
* lock and key theory
* have an active site
* (which) has a specific shape
* shape of active site will only match shape of substrate

• starch is substrate for amylase
• at pH values above or below the optimum the shape of active site
  is changed (in some molecules)
• (so) substrate can no longer fit the active site
• at extreme pH values enzyme is denatured
• (so) shape of active site is changed
• (so) amylase can no longer digest starch
• (so) rate of digestion decreases

Question 22

a student investigated effect of different colours of light on rate of photosynthesis at room temp.
describe how the student should make accurate measurements to obtain valid results for the rate of photosynthesis

Answer 22

-allow pondweed to equillibriate in the light
-use a gas syringe to collect gas/oxygen produced
or use a (measuring) cylinder to
measure oxygen/gas prodcued
measure time oxygen / gas is
collected for using a timer /
stopwatch / stopclock
repeat the measurements and
calculate a mean

Question 23

one presented results as a bar graph other as a graph shwoing wavelength. whats the difference?

Answer 23

independent variable in
student’s investigation is
categoric / discrete

independent variable in
scientist’s investigation is
continuousd

Question 24

describe similarities between benign and malignant tumours

Answer 24

Similarities:
* result from changes in the cell
/ DNA / genes
* uncontrolled cell growth /
division
* can form a lump of cells
* made up of abnormal cells

Question 25

describe differences between benign and malignant tumours

Answer 25

Malignant tumours:
* are made of cancer cells,
benign tumours are not
(usually) grow faster than
benign tumours
* invade neighbouring tissues,
but benign tumours do not
* can spread (to other parts of
the body) but benign tumours
stay in one place
-form secondary tumours but benign cannot

Question 26

there are no new cases of skin cancer diagnosed in people younger than 15. why?

Answer 26

little exposure to ionising
radiation

or

little exposure to carcinogens

(so) less cell / DNA / gene
damage

Question 27

explain the effects on a person if valve develops a leak

Answer 27

some blood would flow back into
the ventricle / heart

(so) less oxygenated blood
would be pumped to the body
cells require oxygen for
respiration
-so person become out of breath/tired