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24/05/2017
OCR Gateway Additional Science
Biology Unit 4 – It’s a
Green World
W Richards
The Weald School
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B4a: Ecology in the local Environment
Taking samples of an ecosystem
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Using different “sampling techniques” we can measure changes
in an ecosystem. The two main measurements are:
1) The physical conditions of a habitat (temperature etc)
2) The populations of different species in that habitat
Some common ways of measuring…
Help!
Measuring
temp, pH etc
Taking animal
samples
Taking samples
using quadrats
Population Size
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There are two ways we can easily use to estimate population size:
Method 1 – Scaling up
If a 1m2 sample contains 10 woodlice how many woodlice are in a field
measuring 200m by 300m?
200m x 300m x 10 woodlice per square metre = 600,000 woodlice
Method 2 – Capture/recapture
A sample contains 10 stoats and a week later a second sample contains 15
stoats of which 2 were in the previous sample. How many stoats are in the
population?
Population Estimate = No. in 1st sample x no. in 2nd sample
Number in 2nd sample previously marked
No. of stoats = (10 x 15) / 2 = 75 stoats
What assumptions are we making with this method?
Ecosystems
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“Ecosystem” is a term used to describe all of the organisms living together
as a community in a particular habitat and can often be self-supporting
other than the need for an energy source.
Ecosystems are constantly changing:
Changes in
population due
to predation,
disease etc
Physical changes
(e.g. temperature
change)
Changes in
ecosystems
Pollution
Changes in soil
conditions
Human
interference
These changes can lead to
“zonation” – a gradual change
in species distribution over
the habitat.
Transect lines and zonation
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Here are some population samples taken along a transect line
along a shoreline:
Ecosystems
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An “Ecosystem” is a physical environment with a particular set
of organisms living in it. They can be natural, e.g. a woodland,
or artificial, e.g. a greenhouse.
A natural ecosystem with
high “biodiversity”
An artifical ecosystem –
biodiversity will be
controlled and low
B4b: Photosynthesis
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Photosynthesis
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Basically, photosynthesis is the process through which a plant
makes its own food using carbon dioxide and water:
That’s a nice plant. I’m
going to put it in the sun and
give it lots of water and air…
CO2
H2O
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Photosynthesis – the 4 things you need
SUNLIGHT
Gives the plant energy
CHLOROPHYLL
WATER
Travels up
from the roots
CARBON DIOXIDE
Enters the leaf through small
holes on the underneath
The green
stuff
where the
chemical
reactions
happen
Photosynthesis equations
Carbon dioxide + _____
Sunlight
Chlorophyll
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glucose + _____
Sunlight
6CO2
+ 6H20
Chlorophyll
C6H12O6 + 6O2
The GLUCOSE produced by photosynthesis is used by the
plant for _______ (through ____________). It is stored
in the plant as ___________.
Words – respiration, starch, water, oxygen, energy
Photosynthesis over the ages
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Our understanding of how plants grow has changed over the ages:
I’m a Greek scientist and we believed that plants
gained mass through taking things in from the soil.
I’m Jean Baptista Van Helmont and I
showed that plant growth wasn’t possible
through nutrient uptake alone.
I’m Joseph Priestley and I proved that oxygen is
produced by plants.
How Photosynthesis works
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Basically, we now understand that the oxygen produced by
photosynthesis comes from water:
1) Light is used to split water, releasing oxygen gas and
hydrogen ions:
HO
H22+O
C6H12O6
2) Carbon dioxide
combines with the
hydrogen ions to
make glucose:
CO2
What is the glucose used for?
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1) Glucose (sugar) can be used to make long chains of insoluble starch…
Glucose
molecules
Starch
molecule
2) Glucose can be used to make cellulose for cell walls…
Glucose
molecules
Cellulose
3) Glucose can be combined with nitrates to make proteins (for growth)…
Glucose
molecules
Proteins
4) Glucose can be converted into lipids (fats or oils) to store in seeds…
Glucose
molecules
Lipid structure
Limiting Photosynthesis
What factors could limit the rate of photosynthesis?
1. Temperature – the best temperature is
about 300C – anything above 400C will
slow photosynthesis right down
2. CO2 – if there is more carbon dioxide
photosynthesis will happen quicker
3. Light – if there is more light
photosynthesis happens faster
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Drawing graphs of these factors
1. Temperature
Photosynthesis is controlled by
enzymes – these are destroyed
at temperatures above 400C
2. Carbon dioxide
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or light
3. Light
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or CO2
Encouraging Photosynthesis
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Using knowledge of limiting factors, explain how plant growth
is encouraged in a greenhouse:
Photosynthesis and Respiration
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In earlier work we looked at respiration:
Glucose
+
oxygen
water
+
carbon dioxide
Photosynthesis is the reverse of respiration:
Water
+
carbon dioxide
glucose
+ oxygen
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Concentration of gas around plant
Gas concentrations over 24 hours
Oxygen
Carbon dioxide
Midnight
Midday
Midnight
B4c: Leaves and Photosynthesis
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Structure of the Leaf
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How do each of the following features help photosynthesis?
Lots of
chlorophyll
Large
surface area
Transparent
Thin
structure
Packed with
chloroplasts
Network of
veins
Lots of air
spaces
Holes
B4d: Diffusion and Osmosis
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Diffusion
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Diffusion is when something travels from an area of high
concentration to an area of low concentration. For example,
consider the scent from a hamburger…
The “scent particles” from
this hamburger are in high
concentration here:
Eventually they will
“diffuse” out into this area
of low concentration:
Oxygen passes into cells by diffusion
Diffusion Summary
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Diffusion is when particles spread from an area of high
concentration to an area of ___ concentration. The particles
move along a “concentration _____” and this process takes no
_____. Diffusion can be accelerated by increasing the
_______ of the particles, which makes them move _______,
or by increasing the surface area of the membrane.
Words – faster, low, gradient, temperature, energy
Osmosis
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Osmosis is a “special kind of ___________”. It’s when water
diffuses from a __________ area to a less concentrated area
through a partially permeable _________ (i.e. one that allows
water to move through but not anything else):
Water
Sugar solution
In this example the water
molecules will move from
left to right (along the
concentration ______) and
gradually _____ the sugar
solution.
Words – membrane, concentrated, dilute, diffusion, gradient
Potato cells
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Strong
sugar
solution
Medium
sugar
solution
Weak
sugar
solution
Osmosis of water from leaves
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Low conc.
of water
Water leaves
the plant by
diffusing
through osmosis
into the air
spaces and then
evaporating.
Low conc.
of water
High conc.
of water
Turgor pressure
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Consider a plant that’s been well watered:
Because there is a _______
concentration of water in the soil than in
the ____, water will enter the plant
cells through _______ and the cells will
become TURGID (“_________”):
In this case the stomata will ______
to allow carbon dioxide in and water
___ and photosynthesis will carry on.
The cell wall prevents the cell from
bursting.
Words: out, swollen, higher, soil, osmosis, open
Turgor pressure
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Consider a plant that’s been badly watered:
Because there is a lower
concentration of water in the soil
than in the plant water will leave the
plant cells through osmosis and the
cells will become FLACCID (“soft”):
In this case the stomata will close to stop
water from escaping through transpiration.
Because they are closed carbon dioxide
cannot get in and so photosynthesis stops.
The cell looks like a deflated balloon – this
is called “plasmolysis”.
Turgid = “tense”
Flaccid = “floppy”
Osmosis in Animal Cells
Animal cells don’t have a cell wall so if
red blood cells are placed in a weaker
solution they swell up, whereas if they
are put in a more concentrated
solution they will shrivel.
If they absorb enough water they will
eventually burst (“lysis”), whereas if
they lose enough water they shrivel up
and become “crenated”. These
differences to plant cells are caused by
the lack of cell wall.
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B4e: Transport in Plants
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Using water
Plants need water to do the following:
Enable
transport
of minerals
Produce
glucose
Form
fruits
Keep the
leaves cool
Enable
growth
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Close up on the stem - Xylem and Phloem
Xylem vessels are made
from dead plant cells and
are used by the plant to
transport water and soluble
mineral salts from the roots
to the stem and the leaves.
Phloem are tubes made
from long columns of living
cells and are used by the
plant to transport dissolved
food to the whole plant for
respiration and storage.
Transpiration
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1) Water evaporates
through the stomata
2) Water passes back into the
leaf through the XYLEM vessels
by osmosis
3) Water is then pulled upwards
through the xylem tissue
4) This is replaced by water
entering from the root tissue
5) Water enters root hair cells by
osmosis to eventually replace the
water lost through respiration
Factors affecting transpiration
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1) High light intensity
This causes the stomata to open thereby
increasing the rate of water loss.
2) High temperatures
This increases the speed of molecule movement
and so speeds up transpiration.
3) Increased wind
This will blow the molecules away and so speeds
up transpiration.
4) High humidity
This decreases the concentration gradient and
so slows transpiration down.
Measuring Transpiration
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The rate of transpiration can be measured using a
“potometer”.
Bung to prevent evaporation
As the plant takes up water
the rate can be measured by
determining the speed of the
bubble.
Water loss
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Water loss through the stomata is biggest on a hot,
dry, windy day. Plants that live in these conditions
often have a thicker waxy layer.
Water loss through leaves
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Carbon dioxide enters a leaf through the ________. These
cells are also responsible for controlling the ______ content
of the ____…
The ______ cells control how wide the
stomata opens (if at all). If too much
water is being lost through the stomata
then the guard cells will _____ to prevent
further loss.
Water and carbon
dioxide enter here
No more water
and carbon
dioxide allowed in
Words – water, close, stomata, guard, leaf
B4f: Plants need Minerals
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Essential Minerals
Nitrates:


Used to make amino acids to form proteins
Lack of it leads to stunted growth
Magnesium:


Used to make chlorophyll for photosynthesis
Lack of it leads to yellow leaves
Phosphates:


Used to make DNA and cell membranes
Lack of it leads to underdeveloped roots and
discoloured leaves
Potassium:


Used to make enzymes for respiration and photosynthesis
Lack of it leads to underdeveloped fruit and flowers
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Active Transport
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Here is a root hair cell:
Now consider the concentration of minerals around the cell:
Mineral
More
concentrated
Less
concentrated
Plants need minerals and ____ and these are “taken up” by
the root hair cell. The _________ of these minerals inside
the cell is ______ than outside so _____ is needed for the
process. This process is called _______ transport.
Words – active, concentration, ions, higher, energy
B4g: Decay
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Recycling ourselves
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Microbes are the key to this – they break down waste and
dead bodies so that the products can be used by plants for
growth. Microbes work best in warm, moist conditions where
there is plenty of oxygen.
More about Decay
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Decay is the process of breaking down complex
structures into ______ ones. This is done be micro
organisms.
The rate of decay is affected by the _______ of these microorganisms:
1) Temperature – the micro organisms’ rates of growth and
respiration are quickest at around 40OC. They become
“_________” at temperatures higher than this.
2) Oxygen – more oxygen means _____ micro organisms.
3) Water – micro organisms grow quickest in ______
conditions.
Words – more, moist, simpler, growth, denatured
Decomposers
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Microorganisms are called “decomposers”. They are used by
humans to help the decay process in compost heaps and sewage
treatment works.
They are helped by earthworms, woodlice and maggots. These
are called “detritivores” – this means they feed on dead
organisms and waste and break it down (i.e. increase the
surface area) to speed up the decay process.
Saprophytes
A “saprophyte” is an organism like
the shiitake mushroom that digests
dead material like dead wood:
This mushroom digests dead wood using “extra-cellular
digestion”, i.e. the food is digested outside of the cell
membrane, often by having enzymes excreted onto it.
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Preventing Food Decay
Food can be preserved by limiting the growth of micro
organisms. Some examples:
1) Using sterile tins/bottle/cans
2) Using a fridge or freezer
3) Pickling the food
4) Adding sugar or salt
5) Dehydrating the food
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B4h: Farming
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Pests
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Crops can be damaged by pests such as herbivorous insects,
weeds and fungal infections. How can the problem be
reduced?
1) Using ________ – these will kill
_____ but they can build up in plants
causing the death of other _______.
2) Introducing natural predators,
such as ______ – not as easy as using
pesticides and would take _______.
Words – ladybirds, animals, insects, longer, pesticides
Biological pest control
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Sometimes a food web can be controlled by the introduction
of a pest, e.g.
Ladybirds feed on aphids
A wasp looking for
caterpillar larvae
What are the advantages and disadvantages of using pests?
Accumulation of pesticides
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Insecticides can wash into a stream or lake where they are
taken up by microscopic water plants. Consider the food chain:
Although the level of insecticides in the plants is small, it
will build up through the food chain due to the number of
organisms in each stage. In this example, if each plant had
“one bit” of pesticide, the bird will have eaten 9 bits.
Intensive Farming
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Some examples of intensive farming:
Battery farms
Fish farms
Hydroponics
Glass houses
Farming Methods
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There are basically two types of farming method; “intensive”
and “organic”:
Intensive
Cost
Produce
Fertilisers
Space
Labour done
by...
Organic
Intensive Farming
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Intensive farming can be used to improve the efficiency of
energy transfer in a food chain by two ways:
1) Get rid of energy transfer to pests or competing weeds
2) Limit an animal’s movement
or keep it warm:
Hydroponics
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Hydroponics basically means “growing plants without soil”.
Advantages
Disadvantages
Mineral levels can
be controlled
Plants have to be
supported
Reduced risk of
disease
Expensive
fertilisers