phot

1. RHS Level 2 Certificate
Week 9 –
Photosynthesis,
respiration, transpiration
and nutrient and water
transport

2. Learning outcomes
1. Photosynthesis and respiration
1.1 State the basic equation for photosynthesis in words.
1.2 Describe how the efficiency of photosynthesis is determined by temperature,
light, carbon dioxide, mineral nutrients and water.
1.3 State the basic equations for aerobic and anaerobic respiration in words.
1.4 Describe how the efficiency of respiration is determined by oxygen, water, and
temperature.
2. Transportation within the plant
2.1 Define the term: ‘transpiration’ and describe how water and minerals move
through the plant.
2.2 Name the tissue that is involved in this process.
2.3 Explain the role of xylem and phloem and describe their location within stems
and roots.
2.4 Describe diffusion and osmosis and their roles within the plant, including
gaseous and liquid diffusion, transpiration, and water uptake
2.5 Describe how stomata control the release of water from the leaf.
2.6 State what is meant by evaporation and how the plant may limit water loss.
2.7 State the effects of relative humidity and temperature on transpiration and water
loss.

4. Photosynthesis
 Carbon
dioxide +water +light → glucose +
oxygen
(when in the presence of
chlorophyll)
Two stages – one of which requires light and
the other does not.

5. The photosynthetic process –light
dependent phase
A
molecule of chlorophyll is excited by a
photon of light and an electron ‘escapes’.
This energy is used to split molecules of
water (H2O) into their component hydrogen
and oxygen. The oxygen is released as a
by-product into the atmosphere.
 The energy released by breaking the
chemical bonds in the water is incorporated,
with the hydrogen, into energy carrying
molecules called ATP and NADPH2

6. e-

7. Photosynthesis – light independent
phase (Calvin-Benson Cycle)
 The
•
energy produced in the light dependent
cycle is used in the chloroplast to convert
carbon dioxide from the atmosphere into
glucose (simple carbohydrate).
This phase takes place both in the day and at
night until the products of the light dependent
phase are used up– it does not need light to
operate.

8. Limiting Factors
 If
a process is influenced by more than
one factor, the rate of the process will
be limited by the factor that is in lowest
supply.
 Limiting factors apply to photosynthesis
and respiration

9. Limiting factors for photosynthesis





Light – only part of the wavelength of light from the
sun is used (PAR – photosynthetically active
radiation).
Carbon dioxide – more than enough of this in the
open air, but under glass may become depleted.
Water –lack of water leads to the stomata closing,
preventing carbon dioxide entering the leaf.
Temperature – the chemical reactions in
photosynthesis are temperature sensitive. Ideal
range 25°C - 36°C.
Nutrients – nutrients from the soil are needed to
make chlorophyll. E.g. magnesium deficient plants
photosynthesise poorly.

10. plateau
At low light intensity, rate of photosynthesis is
proportional to light intensity.

11. plateau
CO2 is a substrate in an
enyme-catalysed lightdependent reaction.
At low CO2 concentration, rate is
positively correlated with concentration

12. Optimum
temperature
Increased temp.
gives increased
energy and
increased rate of
photosynthesis
Above the
optimum temp.,
enzymes are
denatured and
rate drops
steeply.
Which enzymes are
used in respiration?

13. Respiration – in the mitochondria
Glucose + oxygen →carbon dioxide + water+
energy
•Looks
familiar? It’s the chemical equation for
photosynthesis in reverse!
•Anaerobic
fermentation
respiration – does not use oxygen. E.g.
Carbohydrate > (enzymes) = ethanol + carbon
dioxide + energy

14. Limiting factors of respiration
 Temperature
–The ideal range is 36°C
(ideal) down to 0°C.
 Oxygen - aerobic respiration (only)
requires oxygen in sufficient concentration;
reduced oxygen leads to slower respiration.
 Water
loss – closure of stomata due to
water loss prevents oxygen from entering
the plant and slows respiration.

15. Osmosis and diffusion
Osmosis – the movement of water molecules
from an area of high water potential to an area of
low water potential through a semi- permeable
membrane.
 Diffusion - the movement of molecules of a gas
or liquid from an area of high concentration to an
area of relatively low concentration. Note the
difference – no semi-permeable membrane.
 Concentration gradient – the steeper it is the
quicker the movement.


16. Transportation of water and nutrients
 Xylem
– transports water from the roots to
the shoots; enters by osmosis, pushed up a
little way by osmotic pressure and then is
drawn up by transpirational pull. This is a
mechanical process.
 Xylem cells are long, wide and open ended;
dead once mature. Linked end to end and
also laterally through pores called pits

17. Effects of humidity and temperature on
transpiration
 High
humidity =lower transpiration because
the rate of diffusion will fall. This is why
greenhouse growers damp down the floor of
the greenhouse in hot weather.
 The higher the temperature outside the leaf
the more quickly water in the spaces in the
spongy mesophyll will evaporate. The more
water vapour within the leaf the faster the
rate of transpiration through diffusion.

18. Transportation of water and minerals
 Phloem
– transports carbohydrates and plant
growth regulators around the plant from the
leaves.
 Composed of sieve cells which form hollow
living tubes and companion cells which
provide energy to move the sap.
 This active transport means that the
carbohydrates can be moved to parts of the
plant (such as tap root cortex) that are
already rich in these substances.

19. Learning outcomes
1. Photosynthesis and respiration
1.1 State the basic equation for photosynthesis in words.
1.2 Describe how the efficiency of photosynthesis is determined by temperature,
light, carbon dioxide, mineral nutrients and water.
1.3 State the basic equations for aerobic and anaerobic respiration in words.
1.4 Describe how the efficiency of respiration is determined by oxygen, water, and
temperature.
2. Transportation within the plant
2.1 Define the term: ‘transpiration’ and describe how water and minerals move
through the plant.
2.2 Name the tissue that is involved in this process.
2.3 Explain the role of xylem and phloem and describe their location within stems
and roots.
2.4 Describe diffusion and osmosis and their roles within the plant, including
gaseous and liquid diffusion, transpiration, and water uptake
2.5 Describe how stomata control the release of water from the leaf.
2.6 State what is meant by evaporation and how the plant may limit water loss.
2.7 State the effects of relative humidity and temperature on transpiration and water
loss.