Plant development Meristems contain plant stem cells
1) In plants the only cells that are mitotically active are found in plant tissues that are called meristems
2) Meristem tissue is found in the areas of a plant that are growing, such as roots and shoots
3) Meristems produce unspecialised cells that are able to divide and form any cell type in the plant- they act like embryonic stem cells. Unlike human stem ells, these cells can divide for the plants lifespan.
4) The unspecialised cells can become specialised cells and form tissues like xylem and phloem.
5) These tissues can group together to form organs like leaves, roots, stems and flowers. Clones of plants can be produced from cuttings 1) A cutting is part of a plant that has been cut off it
2) cuttings taken from an areas that are growing will contain unspecialised meristems which can make any cell
3) this means a whole new plant can grow from the cutting which will be a clone of the parenting plant.
4) gardeners often take cuttings from parent plants with desirable characteristics and then plant them to produce identical copies of the parent plant. Rooting powder helps cuttings to grow into complete plants
1) if you stick cuttings in the soil they won't always grow
2) if you add rooting powder which contains plant hormones they'll produce roots rapidly and start growing as new plants
3) This helps growers to produce lots of clones of a really good plant quickly. Phototropism Phototropism is growth towards or away from light
1) some parts of a plant, e.g. roots and shoots can respond to light by growing in a certain direction- this is called phototropism
2) shoots are positively phototropic, they grow towards light
3) roots are negatively phototropic, they grow away from light
4) phototropism helps plants to survive. Positive phototropism
Plants need sunlight for photosynthesis. Without sunlight, plants can't photosynthesise, and don't produce food they need for energy and growth. Photosynthesis occurs mainly in the leaves, so its important for plant shoots which will grow leaves, to grow towards light.
Negative phototropism
Plants need nutrients and water from the soil to grow. Negative phototropism means roots grow away from light, down into the soil where they can absorb the water and nutrients the plant needs for a healthy growth

Auxins
Auxins are plant growth hormones
1) Auxins are chemicals that control growth near the tips of shoots and roots
2) Auxins are produced in the tips and diffuse backwards to stimulate the cell elongation process, which occurs in the cells just behind the tip.
3) If the tip of a shoot is removed, no auxins are available and the shoots will stop growing.
4) Auxons are involved in the responses of plants to light, gravity and water. Auxins make shoots grow towards light 1) when a shoot tip is exposed to light, more auxins accumulate on the side that is in the shade that the side thats in the light.
2) this makes the cells grow faster on the shaded side so the shoot grows towards the light.

	Criado por Alice Love mais de 9 anos atrás

Notas sobre B5 - Growth and development, criado por Alice Love em 19-11-2014.