9.3 Growth in plants Flashcards
What is determinate growth?
Growth stops when a certain size has been reached and the structure is fully formed.
This is usually humans and animals, and some plants.
What is indeterminate growth?
Where cells continue to divide indefinitely. Usually most plants have this.
What are meristems?
These are the parts of the plant that growth can occur in. Meristems are composed of undifferentiated cells that are undergoing active cell division. Primary meristems are found at the tips of stems and roots. They are called apical meristems!
What are apical meristems?
Primary meristems which are found at the tips of stems or roots.
How does growth in plants occur?
Cells in the meristems are small and go through the cell cycle repeatedly to produce more cells, by mitosis and cytokinesis. This new cells absorb nutrients and water and so increase in volume and mass.
The root apical meristem is responsible for the growth of the root. The shoot apical meristem is more complex. With each division, one cell remains in the meristem while the other increases in size and differentiates as it is pushed away from the meristem region.
Each apical meristem can give rise to additional meristems including the protoderm, procambium, and ground meristem.
Chemical influences also play a large role in determining which type of specialised tissue arises from unspecialised plant cells.
What does the protoderm do?
It gives rise to the epidermis. It is an additional meristem formed from the apical meristem.
What does the procambium do?
Gives rise to vascular tissue.
What does the ground meristem do?
Gives rise to pith.
What is the leaf primordia?
This is the specialised tissue of a plant that will soon be new leaves, they appear as small bumps. Those small bumps are the leaf primordia.
What controls shoot growth?
Plant hormones control growth in the shoot apex. A hormone is a chemical message that is produced and released in one part of an organism to have an effect in another part. Auxins are hormones that have a broad range of functions including initiating the growth of roots, influencing the development of fruits and regulating leaf development. The most abundant auxin is indole-3-acetic acid (IAA). IAA has a role in the control of growth in the shoot apex. Among other effects, IAA promotes that elongation of cells in stems. IAA is synthesised in the apical meristem of the shoot and is transported down the stem to stimulate growth. At very high concentrations, it can inhibit growth.
What is auxin?
Auxins are hormones that have a broad range of functions including initiating the growth of roots, influencing the development of fruits and regulating leaf development. The most abundant auxin is indole-3-acetic acid (IAA). IAA has a role in the control of growth in the shoot apex. Among other effects, IAA promotes that elongation of cells in stems. IAA is synthesised in the apical meristem of the shoot and is transported down the stem to stimulate growth. At very high concentrations, it can inhibit growth.
Which type of auxin is used?
The most abundant auxin is indole-3-acetic acid (IAA). IAA has a role in the control of growth in the shoot apex. Among other effects, IAA promotes that elongation of cells in stems. IAA is synthesised in the apical meristem of the shoot and is transported down the stem to stimulate growth. At very high concentrations, it can inhibit growth.
What are auxiliary buds?
Auxiliary buds are shoots that form at the junction, or node, of the stem and the base of a leaf. As the shoot apical meristem grows and forms leaves, regions of meristem are left behind at the node. Growth at these nodes is inhibited by auxin produced at the shoot apical meristem. This is termed apical dominance. The further distant a node is from the shoot apical meristem, the lower the concentration of auxin and the less likely that growth in auxiliary buds will be inhibited by auxin. So it stops leaves being formed too close to one another.
How is growth moderated at auxiliary buds?
Auxiliary buds are shoots that form at the junction, or node, of the stem and the base of a leaf. As the shoot apical meristem grows and forms leaves, regions of meristem are left behind at the node. Growth at these nodes is inhibited by auxin produced at the shoot apical meristem. This is termed apical dominance. The further distant a node is from the shoot apical meristem, the lower the concentration of auxin and the less likely that growth in auxiliary buds will be inhibited by auxin. So it stops leaves being formed too close to one another.
In addition, cytokinins, hormones produced at the root promote auxiliary bud growth. The relative ratio of cytokinins to auxins determine whether the auxiliary bud will develop.
How does auxin effect cell growth?
AUXILARY BUDS
- As the shoot apical meristem grows and forms leaves, regions of meristem are left behind at the node. Growth at these nodes is inhibited by auxin produced at the shoot apical meristem. This is termed apical dominance. The further distant a node is from the shoot apical meristem, the lower the concentration of auxin and the less likely that growth in auxiliary buds will be inhibited by auxin. So it stops leaves being formed too close to one another.
GROWING TOWARDS LIGHT
- Higher concentrations of auxin cause greater growth on this side. The cells are elongated.
