- Plants can be classified as aquatic or terrestrial.
- Of the terrestrial plants, there are ones that are vascular and ones that are non-vascular.
- Of the vascular plants, there are seedless plants, and seed-bearing plants
- Of the seed bearing plants, there are gymnosperms and angiosperms
- Angiosperms can be classified as monocots or dicots
Organs
Leaves
Leaves are primarily responsible for photosynthesis. They are covered by cuticles, which are waxy layers that prevent water loss. They have stomata that allow for plants' gas exchange.
Palisade mesophyll are responsible for photosynthesis.
Stems
Stem provide structural support, and they transport of materials between the leaves and the roots.
Roots
Roots are for absorption of water and nutrients, storage of starch, and anchoring the plant to the ground.
They are made up of epidermis, cortex and vascular tissues.
Tissues:
- Meristematic: embryonic tissues. Apical meristem is responsible for primary growth, and lateral meristem is responsible for secondary growth
- Dermal : for protection
- Vascular: for transport. Xylem transports water, and phloem transports nutrients
- Ground: fundamental tissues. Cortex is found in the root and the stem, and it stores starch. Pith is found in the stem, and it stores water
Water and Food Transport
- Glucose is found in leaves, used for cellular respiration
- Sucrose is found in stems (to be transported to leaves or roots)
- Starch is found in roots, stored in the cortex.
- Mechanism: whenever there is photosynthesis and extra glucose, the glucose is transported down to the roots to be stored in starch. The starch is converted back to glucose and transferred back to leaves once they don't have enough
Water transport
Three steps:
- Absorption: Roots absorb water because the cells are in a hypotonic environment. The concentration of minerals in the environment is lower than that in the cells, so osmosis occurs.
- Up the stem: as water and minerals accumulate in the roots, the pressure builds up, so water is pushed up into the roots. There is also capillary action that makes the water goes up.
- Transpiration: as water evaporates from the leaves, the next water molecules is pulled to the top to "replace" the evaporated water molecule. This causes water in the roots to be drawn up as well.
Food transport (translocation)
- Sugars made in the leaves enter the phloem by active transport
- The increased pressure causes the the sugar to be pushed down.
- Sugars then move into storage cell by passive transport
Stimuli
Nastic movement: stimulated response that is not directional
- Turgor response: when certain plants are touched, some of their cells experience water loss and a loss in turgor pressure. This causes a rapid movement.
Tropism: stimulated response that is directional
- thigmotrophism: touch
- phototropism: light
- gravitrophism: gravity
Plant hormones
- Auxin: produced at the apical meristem, it causes vascular tissues to elongate. It causes plants to turn toward the sun and delays the ripening of fruits.
- Cytokinins: promote cell division and differentiation, prevents aging
- Gibberellins: causes elongation of cells and increases the length of stems
- Ethylene: ripens fruit
- Abscisic acid: better colour of fruits
- Oligosaccharin: stimulate plants to produce antibiotics