BIOL1030 Chap.4 Why Plants Matter and How They Are Built
Why Plants Matter and How They Are Built
Why Plants Matter and How They Are Built covers the first two plant lectures of Unit 6 in Week 4. The first makes the case for plants with evidence: discoveries such as the cell, inheritance and transposable elements were first made in plants, plants supply oxygen, food and medicines, and they run large parts of the global carbon and water cycles, with photosynthesis taking up about 123 gigatonnes of carbon a year.
It also sets out the green revolution, slowing yield growth and the threat that heat and drought pose to land carbon uptake. The second lecture builds the plant body from organs to tissue systems to specialised cells, tying every structure to the job it performs.
What this chapter covers
- 01
Discoveries in biology first made in plants
- 02
Plants and human wellbeing: oxygen, food, drugs and energy
- 03
The land carbon budget and rising atmospheric CO2
- 04
Transpiration and the global water cycle
- 05
Roots, stems, leaves and their modified forms
- 06
Dermal, ground and vascular tissue systems
- 07
Parenchyma, collenchyma, sclerenchyma, xylem and phloem cells
Worked example · free
Calculate the net carbon uptake of land plants
- 1Net uptake = photosynthesis minus the two releases: 123 minus 60 minus 60.
- 1Result: about 3 Gt C a year taken up by plants and soils on land.
- 1This sits close to the 3.2 Gt C land sink, so the land balance is a small difference between two very large fluxes.
Key terms
- Harvest index
- The share of a crop's growth that ends up in the harvested part, such as grain.
- Transpiration
- Loss of water vapour from plants to the air, mostly through stomata.
- Ground tissue
- The tissue system, including mesophyll, pith and cortex, that carries out photosynthesis, storage and support.
- Phyllode
- A flattened petiole that does the work of a leaf, as in many Acacia species.
- Collenchyma
- Living cells with unevenly thickened walls that give flexible support to young organs.
Why Plants Matter and How They Are Built FAQ
How much carbon do plants take up each year?
About 123 gigatonnes of carbon a year are taken up through photosynthesis worldwide. Plant respiration and soils each release roughly 60, so the net land uptake is only a few gigatonnes, which is why small shifts in climate can turn forests from sinks into sources.
What changes made the green revolution possible?
Genetics, fertilisers and mechanisation together. In wheat, a dwarfing gene produced shorter plants that spent less on straw and more on grain, raising the harvest index. Yield growth has since slowed to under 1% a year, well below the 2 to 3% needed without farming more land.
What are the three tissue systems in a plant?
Dermal tissue covers and protects the plant and handles exchange with the environment; ground tissue does photosynthesis, storage and support; vascular tissue moves water and minerals in xylem and sugars in phloem. Each runs continuously through roots, stems and leaves.
Why was vascular tissue such an important innovation?
It allowed transport over long distances, so roots and shoots could specialise, one gathering water and nutrients and the other light and carbon dioxide. That division of labour let vascular plants grow taller and larger and come to dominate ecosystems on land.
Why do plants matter for the global water cycle?
Plants move water from the land surface into the atmosphere and influence how much runs off into rivers. The lecture notes that around 90% of water lost from land surfaces leaves through plant transpiration, so changes in vegetation, such as clearing or drought stress, alter both rainfall recycling and river flow.
Exam move
Revise this chapter as numbers plus structures. Make a card with every quantity the first lecture gives, including the carbon fluxes, the 98% oxygen figure, the quarter of prescription drugs and the 90% share of land water loss through transpiration, and practise using two of them as evidence in a short answer.
Then draw a leaf, a stem and a root and label one example of each tissue system and two specialised cell types on each, writing the function beside every label. Finish by explaining one modified organ from each group in a sentence that links its form to its job.
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