Chapter summary
Nutrition and transport in flowering plants, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Leaf structure and gas exchange
How does a leaf bring carbon dioxide close to its chloroplasts?
Key idea and reminders
Stomata and mesophyll air spaces shorten the diffusion route to photosynthesising cells; chloroplast-rich palisade tissue captures light.
- Palisade: many chloroplasts near the upper surface.
- Spongy mesophyll: air spaces and moist exchange surfaces.
- CO2: stoma -> air space -> moist cell wall -> cell -> chloroplast.
Keep in mind: Carbon dioxide reaches mesophyll cells mainly by diffusion through stomata and air spaces. Xylem transports water and mineral ions.
02
Finding xylem and phloem
Which transport tissue is which in a stem or leaf section?
Key idea and reminders
Xylem carries water and mineral ions; phloem carries food, mainly sucrose. Their positions help identify them in a dicot section.
- Stem bundle: xylem nearer centre; phloem nearer outside.
- Leaf vein: xylem above; phloem below.
- Xylem carries water and ions; phloem carries food, mainly sucrose.
Keep in mind: Xylem supplies water and mineral ions; phloem carries food, mainly sucrose. Their main transported materials differ.
03
Root hairs: water and ion uptake
How does one long extension improve absorption?
Key idea and reminders
A root hair increases the absorbing surface in contact with soil water. Water and dissolved mineral ions enter the plant through this surface.
- Long extension -> large area in contact with soil water -> greater absorption.
- Thin wall -> short route to the cell membrane.
- Osmosis names water movement, not movement of mineral ions.
Keep in mind: Osmosis is the movement of water through a partially permeable membrane. Dissolved mineral ions are different substances and their uptake is not osmosis.
04
Photosynthesis makes food
Where do the carbon and energy in a plant's food come from?
Key idea and reminders
Chlorophyll absorbs light energy, which is converted to chemical energy as carbon dioxide and water form carbohydrates and oxygen.
- Carbon in glucose comes from carbon dioxide.
- Light energy becomes chemical energy in food.
- Glucose: respiration, starch, cellulose, sucrose and other organic compounds.
Keep in mind: Carbon dioxide and water supply matter for photosynthesis. Light supplies energy. Roots mainly absorb water and mineral ions; the plant makes organic food.
05
Measuring photosynthesis
What would make a pondweed comparison fair?
Key idea and reminders
Change one factor, control the others and measure oxygen output over a fixed time. Repeated measurements make the comparison more reliable.
- Independent variable: change one factor.
- Dependent variable: oxygen output per unit time.
- Control plant amount, other factors, acclimatisation and timing.
Keep in mind: It can also increase temperature. A fair test must control or monitor this additional change.
06
The transpiration stream
How can evaporation at a leaf move water from the roots?
Key idea and reminders
Water evaporates from mesophyll cell surfaces and diffuses out as vapour. This loss creates a pull that draws water up continuous columns in xylem.
- Evaporation: mesophyll cell walls -> air spaces.
- Diffusion: water vapour -> outside through stomata.
- Transpiration pull: xylem water moves from roots towards leaves.
Keep in mind: Mature xylem vessels are hollow and dead, without functioning cell membranes. Water moves along them by bulk flow; osmosis occurs where water crosses partially permeable membranes elsewhere.
07
Testing transpiration factors
What does a moving potometer bubble actually measure?
Key idea and reminders
A potometer measures water uptake as an estimate of transpiration. Environmental factors change evaporation, the vapour gradient or stomatal opening.
- Potometer = water uptake, used to estimate transpiration.
- Wind and lower humidity steepen the vapour gradient.
- Temperature affects evaporation; light often affects stomatal opening.
Keep in mind: It measures uptake through the apparatus. Uptake is an estimate of transpiration because some water is retained or used in plant processes.
08
When a plant wilts
Why can a plant droop even while its roots are taking up water?
Key idea and reminders
If water loss exceeds uptake, cells lose water and turgor. Soft tissues become flaccid and the plant wilts.
- Compare rates: loss greater than uptake causes a deficit.
- Water loss -> smaller vacuoles -> lower turgor -> drooping.
- Closed stomata conserve water but restrict CO2 entry.
Keep in mind: Wilting can occur whenever water loss exceeds uptake sufficiently. Both processes can still be occurring.
09
Translocation: moving sugars in plants
How can sugars travel down to roots and up to growing shoots?
Key idea and reminders
Translocation moves food, mainly sucrose, through phloem from sources to sinks. Its direction depends on where food is supplied and used or stored.
- Translocation = food, mainly sucrose, transported in phloem.
- Growing and storage regions receive food.
- Translocation and transpiration name different processes.
Keep in mind: That is part of transpiration. Translocation is the movement of food, mainly sucrose, through phloem.