1. Plant physiology, growth and roots
Effects of the environment

2. Do plants eat soil?
It used to be thought that plants got their food from the soil.
This was proved to be untrue by measuring the mass of the soil in a plant pot before and after growth.
The soil did not decrease in mass, even though plant mass increased.
Later experiments showed that plants actually make their own food!
Plants are the only living organisms that can do this.
This means that all other organisms rely on plants.
What is the name of the process by which plants make food?

3. Photosynthesis

4. Photosynthesis + light energy
Plants make their own food by photosynthesis.
light energy
This process is a chemical reaction that uses light energy.
light energy
chlorophyll
carbon dioxide + 
water
oxygen
glucose

5. Photosynthesis

6. Take a look inside a leaf
Teacher notes
This animated zoom activity allows students to investigate how leaves are adapted to photosynthesis on a cellular level. Students could be asked to draw a similar labelled diagram in their books.

7. How do gases enter and leave plants?
On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma. Each stoma is surrounded by two guard cells.
When guard cells gain water, they curve outwards. This opens the stoma, allowing gases in and out.
Losing water causes the guard cells to come closer together, closing the stoma. This stops the movement of gases, but also prevents water loss.

8. Opening and closing of stoma
Teacher notes
This four-stage interactive animation shows how guard cells control the opening and closing of stomata.
Suitable prompts could include:
Start: Where on plants are the stomata?
Stage 1: What liquid enters the guard cells?
Stage 2: Is the concentration of carbon dioxide lower in the air or the plant cells?
Stage 3: Which gas goes out of the stoma in to the air?
What will happen if the plant loses too much water?
Stage 4: How do the guard cells close the stoma?

9. Respiration energy glucose oxygen carbon dioxide water
A chemical reaction that takes place in all living cells.
GLUCOSE reacts with OXYGEN to produce CARBON DIOXIDE and WATER and stored chemical ENERGY is released.

10. Why do trees need energy?
Metabolism
Growth
cell division and expansion
Reproduction
Chemical processes
Mineral uptake
Active transport
Defence

11. How do tall trees get enough water?
The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North!
How does a plant this size get water from its roots to the branches at the top?
Photo credit: © 2007 Jupiterimages Corporation
Transpiration

12. What is transpiration?
Transpiration is the loss of water by evaporation from plants.
Plants lose water when they open the stomata in the leaves to let in carbon dioxide.
Water always moves from an area of high concentration to an area of low concentration. This movement of water is a type of diffusion called osmosis.
Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air.
Teacher notes
See the ‘Movement In and Out of Cells’ presentation for more information about osmosis.
Although it may seem bad for plants, transpiration actually moves water from the roots to the top of the plant, without using energy. How does this work?

13. Transpiration Teacher notes
This four-stage animation uses close-up illustrations of the roots, stem and leaves to show what happens in the different part of a plant during transpiration.
Suitable prompts include:
Start: What is transpiration?
Stage 1: How do root hair cells increase the diffusion of water?
Stage 2: Which plant tissue transports water?
Stage 3: Through what part of the leaf does water evaporats?
Stage 4: What will happen to the water after it has evaporated into the air?
See the ‘Movement In and Out of Cells’ presentation for more information about osmosis and concentration gradients.

14. Roots
Root hairs
Mycorrhizae

15. Water uptake

16. Changing concentrations
During diffusion molecules move from an area of high concentration to an area of low concentration. They are said to move down a concentration gradient.
high
concentration
low
Diffusion is a passive process which means that no energy is needed.
Molecules diffuse until they are evenly spaced apart and equilibrium is reached.
The rate of diffusion depends on several factors, such as the distance the particles have to travel and the difference in concentration.

17. What is osmosis?
Osmosis is the diffusion of water molecules from a low concentration solution to high concentration solution, across a semi-permeable membrane.
A semi-permeable membrane has holes in it that permit water molecules through but are too small to allow larger molecules through.
semi- permeable
membrane
water
glucose

18. Dilute vs. concentrated
During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions.
Dilute solutions have a high concentration of water molecules.
Concentrated solutions have a low concentration of water molecules.
pure water
dilute solution
concentrated
solution

19. Predicting osmosis Teacher notes
This drag and drop activity provides the opportunity for informal assessment of students’ understanding of osmosis.

20. Osmosis in action Teacher notes
This activity could be used as a starter exercise to work on osmosis.

21. What environmental factors will affect the rate of transpiration?
humidity (amount of moisture in the air)
light intensity
temperature
air movement (wind).

22. How do minerals enter plants?
Like water, minerals enter plants through the roots. However, they do this by different methods.
Water passively diffuses with a concentration gradient from the soil into the roots and up the stem.
Minerals are usually found in the soil in lower concentrations than they occur in the plant.
Why can they not be transported by diffusion?
Diffusion cannot take place against a concentration gradient.
Instead, minerals enter the roots by active transport.

23. Active transport in plants
Plants need to absorb mineral elements such as nitrogen, phosphorus and potassium from the soil for healthy growth.
When the concentration of minerals in soil is lower than inside the plant, active transport is used to absorb the minerals against the concentration gradient.
What would happen if the plant relied on diffusion to absorb minerals?
minerals
The cells would become drained of minerals because they would travel down the concentration gradient.

24. What is active transport?
Teacher notes
This two-stage animation shows how substances are transported across the cell membrane. Suitable prompts could include:
Start: What kind of molecules are transported by active transport? (e.g. sodium and potassium in muscle cells)
Stage 1: Which process provides the energy for active transport? (respiration)

25. Which cells transport nutrients?
Plants contain two types of cell adapted for transportation.
Xylem vessels (tracheids in conifers) transport water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only.
Phloem cells (sieve tubes) transport sugars produced in the leaves up
and down the stem to growing and storage tissues.
Both phloem and xylem form continuous systems connecting roots, stems and leaves.

26. How is xylem adapted for transportation?
Xylem vessels have thick cellulose cell walls, strengthened by lignin. The inside of the cell is hollow. Xylem vessels are dead cells.
Xylem vessels transport water and minerals from the roots to the shoot and leaves. This transport only occurs in one direction.
Photo credit: Andrew Syred / Science Photo Library
Coloured scanning electron micrograph (SEM) of a section through the xylem wood vessels of an oak tree (Quercus robur). The water and mineral salts that are absorbed by the roots are conducted through the plant by these tubular cells. Xylem tissue also provides mechanical support. Magnification: x1200 at 6x7cm size.
The thick walls of xylem cells also help support plants.

27. Translocation
Sucrose is pumped in to sieve tube elements by companion cells.
Sucrose loading requires energy.
High sugar concentration in sieve elements (phloem), causes water to flow in.
Pressure builds and sap is forced downwards.
Sugar unloading in roots also uses energy.
Water flows out due to osmosis.

28. Phloem sieve tubes
Living cells

29. Storage Glucose is converted to starch only in living cells.
Starch is insoluble and stored as grains within paranchyma cells (axial and radial) of sapwood and roots.

30. Reproduction

31. Sexual Reproduction

32. Reproduction in conifers

33. Asexual reproduction
Layering
Cuttings
Suckering

34. Germination

35. Requirements for germination
Water
Oxygen
Temperature
Light or darkness
Period of dormancy

36. Dormancy Mechanical Embryonic Hard seed coats
soaking in a solution of sulfuric acid
soaking in hot water or immersing the seed for a short period in boiling water
mechanical scarification
Embryonic
Requires a trigger (usually cold moisture) in order to make it respond.
Cold stratification subject seeds to cold storage in a moist environment

37. Growth

38. Cell division
Cambium cell division

39. Environmental factors affecting growth
Sunlight
Temperature
Water availability
Carbon dioxide
Oxygen
Pollution

40. Sunlight Increased light  increased growth
Plant hormones (auxins) collect on the dark side, so the plant turns to the light

41. Hormones and phototropism
Teacher notes
This animated activity illustrates how auxins act on plant cells in response to light. While viewing the animations it should be highlighted that auxins are produced in the growing tip of the plant but act on the cells below the tip to cause growth through cell elongation. It should also be emphasized that auxins speed growth in shoots but slow down growth in roots.

42. Hormones and geotropism
Teacher notes
This five-stage animation shows a simple experiment that could be used to test how shoots and roots respond to gravity. A broad bean has been used in this animation as they make good test subjects because they germinate quickly.
Suitable prompts include:
Stage 1: How can you investigate the seedlings response to gravity? Stage 2: Where are auxins produced?
Stage 3: How does the shoot respond to gravity?
Stage 4: Does the root respond to gravity in the same way as the shoot?
It should be highlighted to students that auxins speed up growth in the shoots but slow down growth in the roots.
Stage 5: What would happen if the plant did not respond to gravity in this way? Would it be able to survive?

43. Roots

44. Roots
Root hairs
Mycorrhizae

45. How do roots respond to water?
Roots always grow towards water, which is a positive tropism.
Roots will grow sideways, or even upwards, towards water.
Roots always have a stronger response to water than gravity to ensure that a plant gets the water it needs.