TEACHER’S GUIDE
BIOLOGY 2. Form: S3
UNIT 2: TRANSPORT OF MATERIALS
IN PLANTS
Introduction
If plants and animals are to
survive then they must have evolved ways to transport the nutrients to all of their tissues.
The nutrients they use to live and
to grow come from their environment.
In plants the main nutrients are carbon dioxide from the air and minerals from the soil. They use these to make the substances they
need to maintain themselves. In green
plants the carbon dioxide is taken from the air through their leaves. The minerals they need are taken up through their roots, as is water which
is also essential for life.
Animals take in food through their mouths or, in very small organisms, they may be absorbed through
their skin.
The challenge for plants is to
evolve ways to transport their nutrients from the surface of the plant to cells
in the middle of the plant that also need to be nourished. Animals also must
have systems for moving the food they take in to their stomachs or through
their skin (for small organisms) to the rest of their bodies. They must also
have ways to transport waste products out of their bodies.
Very small organisms use a method
called diffusion to move materials.
Nutrients that are dissolved or suspended in water are absorbed through their skins. Once they have been taken in to the
plant or animal, they gradually percolate
or diffuse through their tissues towards the cells in the middle. The problem
is that the rate of diffusion of
substances through the tissues may be slow, so it only works well with small
organisms like protozoa,
single-celled plants and jellyfish. Bigger organisms cannot be kept alive by
diffusion alone, because the cells that are further away from the source of
nutrients would die. So size is a
limiting factor, if the organism depends only on diffusion as its means of
transporting nutrients.
Larger organisms need more complex
systems to transport nutrients around their bodies. In the case of mammals, for
example, they have a heart and blood vessels that allow fluids containing
nutrients to be transported quickly and efficiently.
BRIEF DESCRIPTION OF UNIT OF
TEACHER SUPPORT MATERIAL:
This unit deals with;
- Structure of root hairs and stem.
- Movement of water, minerals, salts and manufactured
food through a transport system.
- Structure and functions of the root hairs, stem and
roots in relation to transport
- Diffusion, osmosis, and plant cell relation:
plasmolysis. Flaccidity and turgidity.
- Active transport
- Opening and closing of stomata
- Transpiration and factors affecting transpiration.
- Translocation
- Storage organs and food nutrients.
SUMMARISE THE MAIN CONTENT AND
CONCEPTS THAT THE TEACHER SHOULD EMPHASISE IN TEACHING THE SUB-TOPIC:
- Transverse section of root, and stem.
- Simple structure of xylem and phloem and relationship
between structure and function.
- Movement of water and solutes from soil to leaves.
- Diffusion, osmosis: Experiments on diffusion and
osmosis.
- Transpiration and factors affecting it.
LIST ITEMS OF TEACHING/LEARNING
MATERIALS:
(Worksheet, stimulus activity, experiments, items of evidence, statistics,
texts, pictures, diagrams, graphs)
Chart with transverse section of a
stem and root, xylem and phloem.
- Knife/razor blade/scapel.
- Microscope, microscopes slide and cover slips.
- Simple potometer, polyethene bag.
- Stain e.g. iodine.
- Anhydrous copper II sulphate/blue cobalt chloride
paper.
- Locally available storage organs (cassava, potatoes,
sugar cane etc.)
- Text books stain e.g. iodine
- Common salt
- Prepared slides of the stem, root, and stomata.
- Animation of diffusion molecules from an area of high
concentration to low concentration.
Worksheet for practical
/experimental activity.
Aim:
To show that a plant transpires.
Materials and apparatus.
-
Potted plant or attached shoot
-
Polythene bag
-
Thread/rubber bands
-
Cobalt chloride paper,/anhydrous copper II sulphate
Procedure
Cover a branch or shoot with a
polythene bag. Tie around the stem with a string or rubber band firmly. (See
diagram below)
Place the set up under sunlight and
leave for 2 hours.
Remove the polyethene bag and
collect the liquid that may have gathered in the bag water.
Test the liquid
with anhydrous copper II sulphate/cobalt chloride paper
Observation:
A colourless liquid collects in the bag.
The white anhydrous powder copper II sulphate
powder turns blue/blue cobalt chloride paper pink/ in the control experiment
there is no water.
Conclusion;
A plant gives off water in form of
vapour
Learners’ activity.
1.
a) Why
isn’t the pot enclosed?
b) Why is the polythene bag tied firmly?
Answers to learner’s activity.
a) To ensure that any moisture that is collected is lost from aerial parts
but not from the soil.
b)
To prevent moisture from the atmosphere getting into
the polythene bag.
Evaluation questions.
- Which of the following tissues conducts water and
also provides mechanical support to a plant
- Phloem
- Xylem
- Cambium
- Cortex
- The figure below shows a transverse section of a
dicot stem. Study it and answer the questions that follow.
a)
Name the parts labeled P to U.
b)
State the functions of each of the parts labeled S and
T.
- State two differences between diffusion and osmosis
1. B
2. a)
P – Cortex
Q - Pith
R
- Cambium
T - Phloem
U – Epidermis
b) S – Conducts water and mineral salts up the plant
T – Conducts manufactured food from
leaves to other parts of a plant.
3.
DIFFUSION
|
OSMOSIS
|
Solutes move from high
concentration to low concentration
|
Water moves from high to low
concentration
|
Membranes not involved
|
Semi-permeable membrane involved
|
Worksheet for practical activity /Experiment II
Aim:
To demonstrate osmosis in living
tissues.
Materials/ and apparatus.
Concentrated solution of
salt/sugar, potato/unripe paw paw.
Procedure:
Peel two potatoes to expose the
living tissue.
Scoop them to form a cup as shown
below.
TEACHER’S GUIDE Include essential teacher information on
separate pages: topic notes, learning objectives, organisational advice and
tips, answers to student exercises, advice on assessment/evaluation, marking
and exam preparation, suggested follow-up and extension work, useful textbook
references and other resources).
References:
- Beckett B.S (1982) Biology: A modern introduction (2nd
Edition) London,
Oxford University Press.
- Hayward.
G. Semakadde I and Ochiro. E. (2002) Macmillan secondary Biology, London, Macmillan.
- Mackean .D.G (1973) Introduction to Biology. London, Evans Brothers, UK.
- Stone R. H and cozens A, B (2002). New Tropical
Biology 3rd edition. London (UK)
Longman
Useful tips:
The teacher should ensure that
control experiments are set up in order to obtain results.
Involve students in suggesting
control experiments.
SAMPLE EXAMINATION
QUESTIONS
SECTION A: OBJECTIVES
- Which of the following processes for movement of
molecules in and out of cells specifically refers to water
molecules?
- Diffusion
- Active transport.
- Osmosis
- Phagocytes
- Which of the following processes requires energy?
- Translocation.
- Diffusion
- Osmosis
- Active transport.
- In which underground organ does cassava store starch?
- Stem tuber.
- Root tuber
- Rhizome
- Corn
SECTION B: STRUCTURED QUESTION
.
1.
The table below shows the distribution of stomata on
the leaves of plants A and B, which live in different habitats. Study the table
and answer the questions that follow:
Leaf
|
No. of stomata
on upper surface
|
No. of stomata
on lower surface
|
A
|
|
02
|
B
|
35
|
100
|
a)
Name the habitat for each leaf.
Leaf A………………………………..
Leaf B………………………………. (2
marks)
b)
i.
State the difference in the distribution of stomata in
plants A and B.
…………………………………………………………………………………
…………………………………………………………………………………
………………………………………………………………………………..
…………………………………………………………………………………
(11/2 marks)
ii.
Give reasons for the difference stated in b (i) above.
………………………………………………………………………………
………………………………………………………………………………..
……………………………………………………………………………….
………………………………………………………………………………..
……………………………………………………………………………….
……………………………………………………………………………….
……………………………………………………………………………….
( 3 marks)
c)
Give the advantages of transpiration to a plant.
……………………………………………………………………………………….
………………………………………………………………………………………
……………………………………………………………………………………..
(2 marks )
d)
State any two adaptations of plants that enable them to
survive in desert areas.
………………………………………………………………………………….
…………………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
(2
marks)
SECTION C: ESSAY/LONG ANSWER QUESTION.
1. a) How does water move from the
soil to xylem of a root? (7
marks)
b) Give the adaptations of root hairs to absorption of water. (2 marks)
c) Name four environmental
factors that affect the rate of transpiration
ANSWERS TO SAMPLE QUESTIONS.
SECTION A
- C
- D
- B
SECTION B
Leaf B – Well-watered soil/land.
b)
i.
The leaves of plant A have more stomata on the upper
than the lower surface whereas the leaves of B have more stomata on the lower
than the upper surface.
ii.
Plant A has more water available to it than plant B. A
needs to lose excess water. B needs to conserve water. In A the stomata are
exposed to direct sunlight, promoting rapid evaporation. In B the stomata are
sheltered from direct sunlight, thus less evaporation.
c) - Cools the
plant.
-Enables absorption of water and mineral
salts.
-Enables upward movement of water and
mineral salts (any two points)
d) - Thick cuticle on leaves to
reduce water loss
-
Leaves modified to spines to reduce water loss.
-
Leaves have small surface area to reduce water loss.
-
Extensive superficial root system to absorb water over
a large area.
-
Deep roots absorb water from deeper layers of soil.
-
Succulent stems or leaves for storage of water.
-
Stomata opening at night and closing during the day to
reduce water loss.
-
Stomata sunken in pits to reduce water loss. (any two points)
SECTION C
1.
(a)
Root hairs absorb water from the soil by osmosis
because the sap in the root hair is more concentrated than the soil solution.
The sap of the root hair cell becomes less concentrated than that of the
neighboring cortical cell, which in turn draws in water from it by osmosis.
Water moves in the same way across the cortex up the xylem vessel. It then
diffuses into the xylem vessel.
(b)
Root hairs are thin and long to increase the surface
area for absorption
Root hairs are
numerous, further increasing the surface area of absorption
(c)
Temperature: High temperatures favour high rates
of transpiration while low temperatures favour low rates.
Relative
humidity: the rate of transpiration is high at low relative humidity and
low at high relative humidity.
Light
intensity: At high light intensity the rate of transpiration is high. At
low light intensity the rate is low
Wind: The
rate of transpiration is higher in windy conditions than in still air.
Atmospheric
pressure: The rate of transpiration is higher at low atmospheric pressure.
Glossary:
Xylem: Tissue that conducts
water and mineral salts from the roots to the leaves.
Phloem: Tissue that conduct
food materials from the leaves to the other parts of a plant
Semi-permeable membrane: /selectively
Is one that allows only solvent
molecules to pass through while preventing the passage of solute molecules.
Flaccid: Describes a cell
that has lost its turgidity and is relatively soft due to loss of water.
Plasmolysis: The loss of
water from a plant cell to the extent that the protoplasm pulls away from the
cell wall. Continued plasmolysis leads to wilting.
Transpiration: Is loss of
water vapour from aerial parts of a plant to the atmosphere.
Occurs mainly through the leaves.
Cohesive force: Is force of
attraction between like molecules or molecules of the same substance.
Adhesive force: Is force of
attraction between unlike molecules or molecules of different substances.
Translocation: Is movement of minerals and chemicals compounds
within a plant
It involves movement of water and mineral
salts through the xylem and manufactured food through the phloem.
Turgor: Is a condition in a plant cell when its
vacuole is distended with water pushing the protoplasm against the cell wall.
Glucose
+ Oxygen
Organisms
obtain food in various ways so as to survive and carry out physiological processes
like respiration, growth, osmo-regulation among others. Organisms having chlorophyll
like plants and protests like Euglena make food by combining inorganic substances
namely water and carbon dioxide to make carbohydrates in a process called photosynthesis.
They use energy from the sun. Some organisms use energy from the oxidation of
certain substances to make food in a process called chemosynthesis.
Organisms that make their own food are referred to as autotrophs.