Plant Organisation and TransportAQA GCSE Biology: Revision notes
Section 1
What tissues make up a plant?
Like animals, plants are organised into tissues, organs and organ systems, each structured to match its function:
- Epidermal tissue — covers the plant surface, protecting it
- Palisade mesophyll — tightly packed cells near the leaf's upper surface, containing many chloroplasts for photosynthesis
- Spongy mesophyll — loosely packed cells with air spaces, allowing gases to diffuse to and from cells
- Xylem and phloem — transport tissues
- Meristem tissue — found at the growing tips of shoots and roots, where growth and cell differentiation occur
Section 2
How is the leaf organised as a plant organ?
The leaf is a plant organ made of several tissues working together: the epidermis (upper and lower), palisade mesophyll, spongy mesophyll, xylem and phloem (in veins), and guard cells surrounding pores called stomata.
This arrangement maximises light capture (palisade layer near the top) and gas exchange (spongy layer with air spaces, connected to the atmosphere via stomata).
Section 3
How are xylem and phloem adapted for transport?
| Tissue | Transports | Direction | Structure | |---|---|---| | Xylem | Water and mineral ions | Roots → stems → leaves (one way) | Hollow tubes strengthened by lignin, forming the transpiration stream | | Phloem | Dissolved sugars (translocation) | Leaves → rest of plant (both directions) | Tubes of elongated living cells connected by pores in their end walls |
Root hair cells greatly increase the surface area of roots, adapted for efficient uptake of water by osmosis and mineral ions by active transport.
Section 4
How do stomata control gas exchange and water loss?
Guard cells change shape to open or close stomata, controlling:
- Gas exchange: carbon dioxide in, oxygen out (for photosynthesis)
- Water loss through transpiration — the evaporation of water from leaf surfaces, replaced by water drawn up through the xylem
Factors that increase the rate of transpiration: higher temperature, lower humidity, greater air movement, and higher light intensity (which causes stomata to open wider for photosynthesis).
Link each transpiration factor to a mechanism: e.g. higher temperature gives water molecules more kinetic energy, increasing evaporation rate.
Must Know
- Plant tissues: epidermis, palisade mesophyll (photosynthesis), spongy mesophyll (gas diffusion), xylem, phloem, meristem (growth)
- The leaf is an organ combining these tissues, with guard cells controlling stomata
- Xylem transports water/minerals one-way (roots→leaves), strengthened by lignin
- Phloem transports sugars both ways (translocation)
- Root hair cells absorb water by osmosis and minerals by active transport
- Transpiration rate increases with higher temperature, lower humidity, more air movement, and higher light intensity
That's the notes covered.
Carry on to the next subtopic.