Growth in plants, making new tissue, does the following- increase the height of plant - allow plant to reach light
-increases width of plant-support plant as it grows taller
produce more leaves- increases amount of photosynthesis
replaces tissue - eaten b herbivore
Germination
Seeds released from a plant can lie inactive (seeds are dormant). Seeds can stay dormant for a number of years until the right conditions
Growth of an embryo plant within a seed is germination
-germination begins with the seed taking in water. This increases the number and speed of chemical reactions occuring in the seed and embryo begins to grow. Oxygen and suitable temperature are also needed
-root of the embryo - radicle- grows first followed by plumule (shoot), As the radicle grows, lateral roots form and root hair develops. Embryo uses stored nutrients in seed to grow seedling.
Once the plumule reaches light, chlorophyll forms and plumule turns green, the seedling can carry out photosynthesis
Factors that affect germination include temperature and the amount of water and oxygen available. Light affects germination of some seeds.
Primary growth
3 processes mitosis (cell division) occurs at growing points such as apical meristem and root tips (increases cell number).
Elongation - occurs behind growing points (cells get bigger)
Differentiation - occurs further away from growing points. Cells change shape to carry out function eg xylem vessel for water transport
diagram
Secondary growth
Plants that live for longer than one or two years grow wider by secondary growth. Secondary growth occurs in the cambium layer - between the xylem and phloem in the vascular tissue
-cells in the cambium layer divide to form new cells. new cells outside the cambium layer become phloem. Older phloem become blocked and cant transport nutrient- become bark
-cells on the inside of the cambium become xylem. older xylem cant transport mineral and become wood.
Xylem formed at different times of the year are different sizes, gives wood a pattern of light and dark bands called annual rings. Xylem produced in spring is usually diameter, giving a light colour wood.
factors affecting growth
Warm temperatures increases the growth rate of plants. High temperatures can slow growth due to water loss. The greater amount of water available in spring and suitable temperatures, result in larger xylem vessels.
The amounts of nutrients in soil or growth media affect growth and photosynthesis. If some nutrients are present in small amounts or not present, photosynthesis slows, slowing growth of plant. eg magnesium needed to make chlorophyll. If soil runs out of magnesium chlorophyll moved to young leaves, older leaves can't carry photosynthesis and may die
Flower development
A plant develops modified leaves called flowers in environmental conditions are suitable. eg some plants flower only if days contain a certain number of daylight hours. A store of nutrients is also needed. in suitable conditions at least four genes known as A,B,C, and D are turned on (expressed) in cells that are to become flowers. The four genes work together to produce four parts taht each flower contains - sepal,petal,stamens and carpel
each flower begins as a disk of cells that develop into four different areas, in circles around the centre. Each area has a different combination of genes that control its development into a flower.
diagram