Transcript Standard Grade Biology Topic 2 The World of Plants World of Plants is divided into: A- Introducing plants B- Growing plants (Pollination, Fertilisation, Asexual reproduction) C-

Standard Grade Biology
Topic 2
The World of Plants
World of Plants is divided into:
A- Introducing plants
B- Growing plants (Pollination,
Fertilisation, Asexual reproduction)
C- Making food
Plants- the first link
Plants are the link between the energy in the sun
being converted into a form which animals can
eat and get the energy to survive…
Workbook Activity
p 54 Food webs and plants
The process by which plants do this is called:
Photosynthesis
All living things respire all the time to release
energy from their food in a process called:
Respiration
Plant survival
Plants make their own food, glucose, by
photosynthesis.
It only happens during the daytime when there is
light available.
carbon dioxide + water
Raw materials

glucose + oxygen
chlorophyll Products
This happens in plant cells containing the chemical
chlorophyll (green-coloured) which traps the light
energy.
The plants have captured light energy and turned it
into a store of chemical energy (glucose).
More on the uses for glucose shortly…
Is light needed for photosynthesis?
1. Take a de-starched geranium plant (24h in dark).
2. Cover part of a leaf with some tin foil (this prevents
light getting through).
3. Leave the plant in sunlight for a few hours.
4. Test the leaf for starch.
Is carbon dioxide needed for
photosynthesis?
1. Take a de-starched
geranium plant
2. Enclose it in a plastic bag
with a chemical that
absorbs carbon dioxide.
(e.g. soda lime or sodium
hydroxide pellets).
3. Leave the plant in
sunlight for a couple of
hours.
4. Test the leaf for starch.
Is light needed for
photosynthesis?
Questions:
1. Which parts of the leaf do you think will go blueblack?
2. Why do parts that were not covered contain starch?
Workbook
Problem Solving
p 81 Making a starch print
Is carbon dioxide needed for
photosynthesis?
Questions:
1. Does the leaf contain starch? Why/ why not?
2. Has the plant carried out photosynthesis?
3. What would be your control plant’s conditions?
(Hint: a control plant should have everything it needs for
photosynthesis including carbon dioxide).
Workbook
Problem Solving
p 76 Plants and greenhouses
CO2 is converted into glucose by photosynthesis.
Mans’ uses of plant glucose
Plants’ uses of plant glucose
Raw material for
growth, repair and
replacement of
damaged parts
To make fats & oils
(energy stored in
seeds)
Energy stored as
sucrose (in fruit)
Energy stored as
starch (in leaves,
seeds, roots and
tubers)
Used immediately to
provide energy
source for respiration
Glucose
Energy used to
turn sugars,
nitrates & other
nutrients into
amino acids
which build up
proteins
To make cellulose,
the main structural
material in cell walls
Glucose molecule
Workbook Activity
p 70 Changes in carbohydrate
Activity
– Testing a plant for sugar
1. Put a piece of raw onion in a pestle and mortar.
2. Grind it with a little sand and 10cm3 of water.
3. Filter the liquid into a test tube
4. Heat the liquid with 10 drops Benedict’s solution in
a water bath
a) What colour change would you expect if sugar
was present?
b) Write an explanation of your results.
You need to know the plant experiments in detail,
explain the different steps, and results, in each one.
Activity
-Testing a leaf for starch
1.
2.
3.
4.
5.
6.
7.
Dip a leaf into boiling water for
about a minute (to soften it).
Turn off the Bunsen burner.
Put the leaf into a test-tube of
ethanol (to remove chlorophyll).
Stand the test-tube in a beaker of
hot water for about 10 minutes.
Wash the leaf in cold water.
Spread the leaf out flat on a petri
dish and cover it with iodine
solution (tests for starch).
If the leaf goes blue-black,
starch is present.
Activity
-Testing a leaf for chlorophyll
Repeat the starch test
but this time use a
variegated leaf from a
geranium plant.
Variegated means that a
plant has coloured and
white parts on its leaves.
Do the green parts
contain chlorophyll? Do
the white bits? Which do
you think will test
positive for starch?
From little acorns do great
oaks grow…
A tree is planted in a meadow.
After 20 years it has grown into a big tree,
weighing 250kg more than when it was planted.
 Where do the extra
250kg come from?
 Explain your
answer as fully and
scientifically as you
can.
Gas Balance
all the time
glucose + oxygen  carbon dioxide (CO2) + water
daylight only
carbon dioxide + water

glucose + oxygen
During the day:
Oxygen released by photosynthesis is greater than
the amount of oxygen used up in respiration.
CO2 used in photosynthesis is greater than the
amount of CO2 produced by respiration.
Fill a jar with water.
Fill a test tube with water too
and cover the top as you
place it upside down inside
the jar.
Take a runner and feed it up
inside the test tube.
Leave in direct sunlight for a
few hours
Result?
A bubble of oxygen gas should
form at the top of the test tube as it
photosynthesises
Summary of Photosynthesis
Plants’ waste productoxygen- is essential for
animal life.
Workbook Activity
p 64-65 Elodea bubbler expt
Quick Quiz 1
1. What does a plant need for photosynthesis?
Carbon dioxide, water, chlorophyll, light.
2. What does a leaf produce during photosynthesis?
Oxygen, glucose
3. What is chlorophyll?
A green pigment which absorbs the sun’s energy
4. How do the leaves obtain water?
Through the roots (and xylem tubes by osmosis
5. How does the plant obtain carbon dioxide?
From the air (through stomata)
6. List 3 uses of the glucose produced by
photosynthesis?
Cellulose (structural), starch (storage), energy
7. Name the storage form of carbohydrate in a leaf.
Starch.
A leaf in time
Library activity
Read through the file and
take some short notes to
summarise the life of a leaf
http://www.portlandpress.com/pp/books/online/leaf/
alit_eng.pdf
Source: http://www.life.uiuc.edu/plantbio/102/links.html
Leaves…
Leaves are the
organs of
photosynthesis
and make all the
food for a plant.
We will look at:
 Outer layers
(top & bottom)
 Inner structure
including veins
(its transport
system)
Internal structure
waxy cuticle
mesophyll
Collect the handout ‘Leaf structure’ and add labels/notes.
Outer layer- upper surface
1.waxy
2.
1. The waxy cuticle is a waterproof layer which cuts
down water loss by evaporation.
2. The upper cells of the leaf make up the epidermis.
They are transparent so light passes straight through
them into the next layer of cells…
The palisade
layer contains
cells with lots of
chloroplasts.
mesophyll
Chloroplasts
contain chlorophyll
which is the
chemical which
absorbs the sun’s
light energy.
Hence this is
where most
photosynthesis
occurs.
The spongy layer (spongy
mesophyll) contains rounded cells
with many air spaces allowing CO2
to circulate and reach the palisade
cells, while O2 leaves.
Workbook Activities
p 66-67
Leaf surface and thickness
p67
Leaf layer cards- matching
Problem Solving
p78 How many stomata?
p79 Water content and dry weight.
p85 Use of cobalt choride paper
Bioviewers
The leaf of a flowering plant
Box 79
Outer layer- bottom surface
Leaf epidermis with stomata- scanning electron microscope
On the lower surface of the
leaf there are tiny pores
called stomata (singularstoma) which open and
close.
Stomata let CO2
diffuse in.
Water vapour and
oxygen (O2) move
out.
Stomata- open
Stomata have guard cells surrounding
them to control their opening & closing.
When there is
plenty of water
(daytime) the
guard cells are
turgid and curved.
This opens the
stomata and water
can escape.
Workbook
p 62 Leaf surfaces
Stomata- closed
When there is
little water the
guard cells are
flaccid and less
curved.
This closes the
stomata and
keeps water in
the leaf. This
happens at night.
Workbook Activity
p63 stomata behaviour
PS
p82 & 83 Leaf balance
General
structure
Flat leaf blade
Thin
Has large surface area
CO2, reaches inner
cells easily
Absorbs as much sunlight
& CO2 as possible
Vast network of veins
Stomata
supplies all parts of the plant
with essential substances
Most in lower surface
of leaf
Structural support
Gas & water exchange
Leaf veins
Leaf veins (and roots and stems) contain the xylem and
phloem tubes in vascular bundles.
They run throughout the plant, transporting various
substances up and down them.
Workbook
Problem Solving
p 80 Ringing a plant
Transport systems used for?
Plants need to allow:
 Gases to get in and out
of the leaves.
 Water and nutrients to
move into the plant from the
soil.
 Glucose made in
photosynthesis to be carried
to the rest of the plant.
Workbook Activity
p 61 Food transport diagram
Giant redwood trees carry water & nutrients over 100m from the soil
Roots
 Roots have specialised cells called root hair
cells, which are long and thin providing a large
surface area for the uptake of water and minerals.
Into the root hair cell
Water passes from the soil into
root hairs by osmosis
DEFINITION
 Osmosis is the net diffusion of water across a
partially permeable membrane, from a solution
with a high water concentration (HWC) to one
with a low water concentration (LWC).
HOW DOES IT HAPPEN?
 The water in the soil has a weak solution of salts
 The cell sap has a more concentrated solution
 Water moves from the soil into the root hair
along a water concentration gradient
Osmosis
Osmosis
 When water moves into a plant cell by osmosis it
increases the pressure inside the cell.
 The cell walls are sufficiently strong to withstand the
pressure.
 It is this pressure which keeps the cells rigid
(maintains their turgor) and provides support.
Transpiration is the evaporation of
water from the leaves of a plant.
The transpiration stream is the
movement of water up the xylem
(roots-stem-leaves).
Functions 1. Anchoring the plant
Why?
So it is not blown / knocked over
How?
The roots spread out over a large area
to counterbalance the structures above the soil.
This also helps plants find water.
2. Absorb essential nutrients
Why?
How?
To take up substances to survive.
Roots have tiny hairs on their surface which
increases their surface area to maximise absorption.
Many tiny hairs branch off the main root
3. Absorb water
A root hair shown
under a microscope
Root hair cell
Root hair
Why?
How?
Water is a raw material for photosynthesis.
Root hairs increase surface area.
Transport in Flowering Plants
In flowering plants there are separate transport
systems for water and nutrients.
Substances are transported in vascular bundles
made up of the xylem and the phloem.
Xylem Tissue
Transports water and
minerals upwards from the
roots to the stem and
leaves.
The Xylem is made of dead
cells joined into hollow
tubes. They have thick
strong walls made of lignin
which give the plant support.
Phloem tissue
Phloem tissue
Carries nutrients,
e.g. sugars made by
photosynthesis, all
round the plant.
The sugars are
transported all round
the plant especially to
growing regions and
the storage organs.
Phloem cells are alive and are made of 2 types of
cells; sieve tubes and companion cells.
Sieve cell end walls have holes (pores) in them.
Companion cells contain the cell nuclei.
Sugar cane
Leaf Veins are Vascular Bundles.
Vascular bundles
are composed of
Xylem, Phloem and
Fibres which support
and protect the
xylem and phloem.
Workbook Activity
p 72 Structure of xylem and phloem.
Vascular bundles
Vascular
Bundles in
sugar cane.
Left: crosssection
Below: detail of
one bundle
Workbook Activity
p 73 Looking at xylem
Xylem & phloem in stem
Bioviewers
Box 78 Workbook Activity
The stem of a flowering plant
p 60 Water transport in plants
Position of vascular tissue in the stem
The positions are different in stems compared to
roots. In a stem they are round the outside.
epidermis
xylem
phloem
Position of vascular tissues in the roots
epidermis
xylem
phloem
In roots they are found
in the centre.
Workbook Activity
p 68-69 Structure stem, root
What Limits photosynthesis?
Carbon dioxide + water
Light + chlorophyll
oxygen + glucose
Ingredients
 For photosynthesis to happen all the “ingredients”
need to be present.
If there are inadequate ingredients photosynthesis will
stop or slow down.
 The factor that is in shortest supply will be the
one that limits the rate of photosynthesis and is
called a “limiting factor”.
Factors limiting photosynthesis
 Low temperature
 Shortage of CO2
 Shortage of light
 Lack of chlorophyll
Example:
 A plant has plenty of water, carbon dioxide and
chlorophyll, but it is night.
Hence, photosynthesis cannot take place due to
lack of light.
Light is the limiting factor.
Often this sort of information is shown in a graph…
A
B
A Light intensity is
limiting the rate of
reaction
C B CO is limiting
2
Rate
the rate of
reaction
C The difference
Light intensity
between the lines
is due to different
temperatures.
Workbook Activity
p 74 The effect of increasing carbon dioxide
p75 The effect of increasing temperature
Quick Quiz 2
1. How is glucose carried from the leaves to every
part of the plant?
Transported in phloem tubes (water in xylem)
2. Give 2 structural features of a leaf that make it a
good design for photosynthesis.
Large surface area, thin, stomata, veins
3. Why do you think that the palisade cells are near
the surface of the leaf?
To absorb as much sunlight as possible in chloroplasts
4. Name the cells that surround the stomatal openings.
Guard cells
5. The spongy mesophyll cells are loosely arranged.
Explain the significance of this.
Large spaces between cells allow gases to diffuse quickly
6. Which 3 factors limit the rate of photosynthesis?
Quantity of light, carbon dioxide, temperature
Helping plants to grow
 Plants need mineral salts from the soil for healthy
growth. In nature, plants die, decompose and
mineral salts return to the ground.
 When crops are harvested, the plants are removed,
there is no decomposition, and the quality of the soil
decreases as less nutrients become available.

Manufactured fertilisers are added to the soil to
replace those that are lost. This enables healthy
crops to grow quickly, but at a cost to the farmer.
Questions
1. Why do farmers want to harvest crops quickly?
2. What do fertilisers contain to help plants grow?
Signs of Nutrient deficiency in plants
Lack of Nitrogen
causes ..
1. Yellowing of
leaves.
2. leaves on lower
parts of the plant
may die
3. Weak stem
meaning the plant
cannot grow tall.
Lack of Potassium causes ….
1. Yellowing
of leaves
2. Poor fruit
growth.
Lack of Magnesium causes leaves to turn
yellow from the bottom of the plant upwards
Leaf
from
the
bottom
of a
plant
Leaf
from
the top
of a
plant
Lack of Phosphorus causes ….
1. Purpling of leaves
2. Poor root growth
3. Small plant size
Copy out the
diagrams from p63
Co-ordinated
Biology (second
Edition) showing
nutrient deficiency
in plants
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