tropic responeses
Tropism- growth response of a plant to an external stimulus
3 main types of tropism are phototropism, gravitropism, and thigmotropism
Thigmotropism is a growth response to mechanical stimuli, such as contrast with an object, another organism or even wind. thigmotropism is evident in vines that twist around a nearby structure such as a fence or tree.
gravitropism is a growth response to gravity, roots generally show a positive gravitropism. The downward growth of roots into soil helps to anchor the plant and brings roots in contact with water and minerals. However, a stem exhibits a negative gravitropism when it grows upwards, pushing against gravity. this growth position leaves for maximum exposure to light.
phototropism is a growth response to light caused by an unequal distribution of auxin
if plant growth is away from stimulus, it is negative tropism
if plant growth is towards stimulus, its positive tropism
Abscisic Acid
blocks the action of growth promoting hormones
blocks the intakes of carbon dioxide by controlling the opening and closing of leaf stomata
generally inhibits growth
Ethylene
weakens the cell walls and break downs complex carbohydrates
can effect other parts of plants, mainly affects ripening fruits
transported within the phloem
is in the ripening fruits or dying leaves and plants
known as gaseous hormones
Gibberellins
promote growth of taller stronger plants and plants that flower early
they stimulate plant growth by changing cell walls
transported in the vascular tissue
produced in the apical meristem and there are many kinds
Cytokinins
cytokinins also delay the ageing of leaves and fruit
promote cell division and differentiation by stimualting the production of the proteins neeeded for mitosis and cytokinesis
Auxins
effects of auxins in a plant varies depending on its concentration and location
auxins produced by the apical dominance, which is a condition of a plant stem in which growth is mainly upward, with little growth laterally from side branches
is a group of compounds that stimulate the elongation of plant cells
Vascular
they are dominant sporophyte plants
Non Vascular
they are dominant gametophyte plants
PLANT GROWTH AND REPRODUCTION
Plant Growth
plant harmones are rarely independent
5 main harmones are auxins, cytokinins, gibberellins, ethylene, and abscisic acid
plants produce chemical compounds which are called harmones
Plant Reproduction
Have 2 types of reproductions which is asexual and sexual
asexual
reproduction that only requires one parent and produces genetically identical offspring
sexual -
is the reproduction that requires 2 parents and produces genetically distinct offspring
Asexual
artificial propagation
an example of this would be splitting, grafting, cutting and layering tissues
natural vegetative propagation
the growth happens in the roots, to the stems and the leaves
Sexsual
sporic reproduction which is an alternation of generations
seed plants
angiosperms
double fertilisation occurs
wind, insect or animal pollination
protected seeds develop within the ovary wall
gymnosperms
single fertilisation occurs
wind pollination occurs
they are unprotected seeds that develop on upper surface of reproductive structures
seedless plants
they have unprotected zygote, embryo and gametophytes
they are independent gametophytes plants
they are a swimming sperm
they are adapted for reproduction in wet environments
