3.1.2 Packed with chloroplasts for
photosynthesis. more of them are
crammed on the top of the cell -
so they are closer to the light
3.1.3 Tall shape means a lot of
surface area exposed down
the side for absorbing CO2
from the air in the leaf.
3.1.4 Thin shape means that you
can pack loads of them in
at the top of a leaf.
3.2 Guard Cells
3.2.1 They are
open and close
3.2.2 Special kidney shape
which opens and
closes the stomata
(pores) in the leaf
3.2.3 When the plant has lots of water the
guard cells fill with it and go plump and
turgid, this makes the stomata open so
gases can be exchanged for photosynthesis
3.2.4 When the plant is short of water, the
guard cells lose water and become flaccid,
making the stomata close. This helps to
stop too much water vapor from excaping
3.2.5 Thin outer walls and
thickened inner walls
make the opening and
3.2.6 They're also sensitive to
light and close at night to
save water without loosing
out on photosynthesis.
3.2.7 Guard cells are adapted to
their function of allowing gas
exchange and controlling
water loss within the leaf.
3.3 Red Blood
3.3.1 They are
3.3.2 Their concave shape gives a big
surface area for absorbing oxygen. It
also helps them pass smoothly
through capillaries to reach body cells.
3.3.3 They are packed with
haemoglobin - the pigment that
absorbs the oxygen.
3.3.4 They have no
nucleus, to leave
more room for
3.4 Sperm and Egg
3.4.1 They are specialised for reproducton
and are very important.
3.4.2 The main function of an egg cell are to
carry the female DNA and to nourish
the developing embryo in the early
stages. The egg cell contains huge food
reserves to feed the embryo.
3.4.3 When the sperm fuses with the
egg, the egg's membrane instantly
changes its structure to stop
anymore sperm from getting in.
This makes sure the offspring ends
up with the right amount of DNA.
3.4.4 The function of the sperm is basically to get
the male DNA to the female DNA. It has a long
tale and a streamline head to help it swim to
the egg. There are a lot of mitochondria in the
cell to provide the energy needed.
3.4.5 Sperm also carry
enzymes in their
head to digest
through the egg cell
5.1 Plant Cells Are Organised Into
Tissues And Organs
5.1.1 Plants are made of organs like
stems, roots and leaves. These
organs are made of tissues. For
example leaves are made of:
22.214.171.124 Mesophyll tissue -
this is where most of
the photosynthesis in
a plant occurs.
126.96.36.199 Xylem and phoem - they transport
things like mater, mineral irons
and sucrose around the plant.
188.8.131.52 Epidermal tissue - this
covers the whole plant.
5.2 Photosynthesis Equation
5.3 Photosynthesis produces
glucose using sunlight
5.3.1 Photosynthesis is the process that
produces 'food' in plants and algae.
the 'food' it produces is glucose.
5.3.2 Photosynthesis happens
inside the chloroplast.
5.3.3 Chloroplast contains a green substance called
chlorophyll, which absorbs sunlight and uses
its energy to convert carbon dioxide (from the
air) and water (from the soil) into glucose.
Oxygen is also produced as a by-product.
5.3.4 Photosynthesis happens
in the leaves of all green
plants - this is largely
what the leaves are for,
5.3.5 The cross section of a
leaf showing the four
raw materials needed
6.2 The rate of photosynthesis is affected by the intensity of
light, the volume of CO2, and the temperature. Plants also
need water for photosynthesis, but when a plant is short
of water it becomes the limiting factor in photosynthesis,
its already in such trouble that this is the least of its
6.3 The Limiting Factor
Depends On Conditions
6.3.1 Any three factors that affect
photosynthesis can become a limiting
factor. This just means that it's stopping
photosynthesis from happening any faster.
6.3.2 Which factor is limiting at a
particular time depends on
the environmental conditions:
184.108.40.206 At night it's pretty obvious
that light is the limiting factor.
220.127.116.11 In water it's often
18.104.22.168 If it's warm enough and
bright enough, the amount
of CO2 is usually limited.
6.4 Three Important Graphs
For Rate Of Photosynthesis
6.4.1 Not Enough Light Slows
22.214.171.124 Light provides the energy
needed for photosynthesis
126.96.36.199 As the light level is raised, the rate
of photosynthesis increases steadily
- but only up to a certain point.
188.8.131.52 Beyond that, it wouldn't make any difference
because then it'll be either the temperature or
the CO2 level which will be the limiting factor.
184.108.40.206 In the lab you can change the light intensity by moving a
lamp closer to or further away from the plant.
220.127.116.11 But if you just plot the rate of photosynthesis against "distance of
light from the beaker" you get a weird shaped graph. To get the ideal
graph you either need to measure the light intensity at the beaker
using a light meter or do a bit of nifty maths with your results.
6.4.2 Too Little Carbon Dioxide
18.104.22.168 CO2 is one of the raw
materials needed for
22.214.171.124 As with light intensity the amount of
CO2 will only increase the amount of
photosynthesis up to a point. After this
the graph flattens out showing that
CO2 is no longer the limiting factor.
126.96.36.199 As long as light and CO2 are in
plentiful supply then the factor limiting
photosynthesis must be temperature.
188.8.131.52 There are lots of different ways to control the amount of CO2. one way is to dissolve
different amounts of sodium hydrogencarbonate in the water which gives off CO2.
6.4.3 The Temperature
Has To Be Just Right
184.108.40.206 Usually, if the temperature is
the limiting factor it's because
it's too low - the enzymes
needed for photosynthesis work
slower at low temperatures.
220.127.116.11 But if the plant gets too
hot, the enzymes will get
damaged or denatured.
18.104.22.168 Enzymes often get
damaged at about 45°C
22.214.171.124 Experimentally, the best
way to control the
temperature of a flask is
to put it in a water bath.
6.5 You Can Artificially Create The
Ideal Conditions For Farming
6.5.1 The most common way to
artificially create the ideal
environment for plants is to
grow them in a green house.
6.5.2 Greenhouses help to trap the sun's heat,
and make sure that the temperature
doesn't become limiting. In winter a
farmer or gardener might use a heater
as well to keep the temperature at the
ideal level. In the summer it could get too
hot, so they might use shades and
ventilation to cool things down.
6.5.3 Light is always
often supply artificial
light after the sun
goes down to give their
plants more quality
6.5.4 Farmers and gardeners can also
increase the level of CO2 in the
greenhouse. A fairly common was is
to use a paraffin heater to heat the
greenhouse. As the paraffin burns
it makes CO2 as a by-product.
6.5.5 Keeping plants enclosed in a greenhouse also makes it easier to keep
it free from pests and diseases. The farmer can also add fertilisers to
the soil as well, to provide all the minerals needed for healthy growth.
6.5.6 Sorting all this out costs money - but if
the farmer can keep the conditions just
right for photosynthesis. the plants will
row much faster and a decent crop can be
harvested much more often, which can
then be sold. It's important that the
farmer supplies the right amount of heat,
light, etc. - enough to make the plants
grow well, but not more than the plant
needs, as that would be wasting money.
7.1.1 1) Plants manufacture
glucose in their leaves.
7.1.2 2) They then use some of
the glucose for respiration.
7.1.3 3) This releases energy which
enables them to convert the rest
of the glucose into various other
useful substances, which they can
use to build new cells and grow.
7.1.4 To produce so,me of the other substances they
also need to gather a few minerals from the soil.
7.2 Making New
7.2.1 Glucose is converted into cellulose for making strong
cell walls, especially in a rapidly growing plant.
7.3.1 Glucose is combined with nitrate ions to make
amino acids, which are them made into proteins.
7.4 Stored In Seeds
7.4.1 Glucose is turned into lipids for storing in seeds, Sunflower seeds for example, contain
a lot of oil- we get cooking oil and margarine from them. Seeds also store starch
7.5 Stored As
7.5.1 Glucose is turned into starch and stored in roots, stems and leaves, ready for use when
photosynthesis isn't happening. like in winter. Starch is insoluble which makes it much better
for storing than glucose - a cell with lots of glucose in would draw lots of water and swell up.
8 Distribution of organisms
8.1 Organisms live in
different places because
the environment varies
8.1.1 A habitat is a place
where an organism
lives, e.g. a playing field.
8.1.2 The distribution of an organism
is where an organism is found,
e.g. in a part of the playing field.
8.1.3 Where an organism is found is affected
by environmental factors such as:
126.96.36.199 Oxygen and carbon
188.8.131.52 Amount of
8.1.4 An organism might be more
common in one area than
another due to differences in
environmental factors between
the two areas. For example, in
a field, you might find that
daisies are more common in in
the open, than under trees,
because there is more light
available in the open.
8.1.5 There are a couple of
ways to study the
distribution of an
organism. you can:
184.108.40.206 Measure how common an organism
is in two sample areas (e.g. using
quadrats) and compare them.
220.127.116.11 Study how the distribution changes across an
area e.g. by placing quadrats along a transect.
8.2 Use Quadrats To Study The
Distribution Of Small Organisms.
8.2.1 A quadrat is a square frame
enclosing a known area, e.g. 1m². to
compare how common an
organism is in two sample areas.
8.2.2 1) place a 1m² quadrat on the
ground at a random point
within the first sample area.
8.2.3 2) count all the organisms
within the quadrat.
8.2.4 3) Repeat stops 1 and 2 as
many times as possible.
8.2.5 4) Work out the mean number of organisms
per quadrat within the first sample area.
8.2.6 5) Repeat steps 1-4 in
the second sample area.
8.2.7 6) finally compare the two means.
E.g. you might find 2 daisies per
m² in the shade, and 22 daisies
per m² in the open field.
8.3 Working Out
8.3.1 1) Work out the mean
number of organisms per m²
8.3.2 2) Then multiply the mean by the
total area (in m²) of the habitat.
18.104.22.168 E.g. if the area of an open field is 800 m², and there are
22 daisies per m², then the size of the daisy population is
22 X 800 = 17,600
8.4 Use Transects to study the
distribution of organisms along a line.
8.4.1 You can use lines called transects to help
find out how organisms are distributed
across an ares - e.g. if an organism because
more or less common as you move from
hedge towards the middle of a field.
22.214.171.124 1) Mark out a line in the
area you want to study
using a tape measure.
126.96.36.199 2) Then collect
data along the line.
188.8.131.52 3) You can do this by just counting
all the organisms that you're
interested in that touch the line.
184.108.40.206 4) Or you could collect data by using quadrats.
These can be placed next to each other along
the line or at intervals, for example, every 2 m.
8.5 When Collecting Environmental
Data You Need To Think About...
220.127.116.11 1) Quadrats and transects are
pretty good tools for finding out
how an organism is distributed.
18.104.22.168 2) But you have to work
hard to make sure that
your results are reliable -
which means making
sure they are reproducible
22.214.171.124 3) To make your results more reliable you need
to take a large sample size, e.g. use as many
quadrats and transects as possible in your
sample area. Bigger samples are more
representative of the whole population.
126.96.36.199 1) For your results to
be valid they must be
reliable and answer
the original question.
188.8.131.52 2) to answer the
you need to control
all the variables.
184.108.40.206 3) The question you
want to answer is
whether a difference in
two sample areas is due
to a difference in the
220.127.116.11 4) If you've controlled
all the other variables
that could be affecting
the distribution, you'll
know whether a
distribution is caused
by an environmental
factor or not.
18.104.22.168 5) IF you don't control the other variables you won't
know whether any correlation you've found is
because of chance, because of the environmental
factor you're looking at or because of a different
variable - the study won't give any valid data.
22.214.171.124 6) Use random samples,
e.g. randomly put down
or mark out your
quadrat or transect. If all
your samples are in one
spot, and everywhere else
is different, the results
you get wouldn't be valid.