Responding to the environment: Plants Flashcards
What are plant hormones?
Molecules that are produced naturally within plants.
Do plant hormones occur in high or low concentrations?
Low concentrations
What do plant hormones do?
Regulate the processes within the plant:
- In cells and tissues, they influence:
- growth
- development
- differentiation
- Determine:
- formation of:
- flowers
- stems
- leaves
- shedding of leaves
- development and ripening of fruit
- formation of:
Do all plant cells respond to hormones?
No
Name the three different classes of plant hormones
- Abscisic acid
- gibberellins
- auxins
Where do auxins occur in the plant?
In the:
- Embryo of seed
- Young leaves
- Young fruit
- Meristems of apical buds
What are some of the major functions of auxins?
- Stimulate:
- cell elongation
- ethylene synthesis
- fruit development
- adventitious roots on cuttings
- Tropic responses (phototropism and geotropism)
- In vascular tissue, maintains:
- apical dominance
- differentiation
- Inhibits flowering
- Abscission before formation of abscission layer
- Controls:
- ageing
- senescence
- dormancy of seeds
Where does abscisic acid occur in plants?
- leaves
- stems
- green fruit
What are some of the major functions of abscisic acid?
- Stomatal closure
- inhibits cell growth
- dormancy
Where is gibberellin found?
- meristems of apical buds
- roots
- young leaves
- embryo
What are some of the major functions of gibberellin?
- cell division
- cell elongation
- shoot elongation
- seed germination
- flowering in biennials
- production of hydrolytic enzymes (in grains)
- development of male flowers in monoecious plants
What do herbicides contain?
a synthetic plant growth hormone or auxin
Chemically, what are auxins or plant growth hormones classified as?
acids
In what form are herbicides applied?
Ester or salt form
What do herbicides induce?
Uncontrolled plant growth
What are broad-leaf plants called?
dicotyledons
Give one example of a dicotyledon
dandelions
A dicotyledon is a broad-leaf plant
What are narrow-leaf plants called?
monocotyledons
Give two examples of monocotyledons
grasses
cereal crops
Monocotyledons are narrow-leaf plants
Which are more susceptable to auxins, dicotyledons or monocotyledons?
dicotyledons
What are normally dicotyledons?
weeds
What are SELECTIVE HERBICIDES or SELECTIVE WEED KILLERS?
Herbicides that kill some plants, but not others
That are collectively called growth substances
What is the most important group of chemicals for plant growth?
Auxins
Where are auxins produced?
In the meristematic region of the growth tip of a:
- shoot or root
- plant embryo
- young fruit
- young leaves
Auxins move away from a…
Unidirectional light source
Auxins are attracted by…
The force of gravity
When auxins occur in the correct concentration, they…
- stimulate cell division
- stimulate cell elongation
What is phototropism?
The growth response of a plant to a light source
What is the growth response of a plant to light source due to?
An unequal distribution of auxins in the stem tip when exposed to a light source from one direction
What is positive phototropism? Where does it occur?
- Growth towards a light source
- Plant stems
What is negative phototropism? Where does it occur?
- Growth away from a light source
- In plant roots
Auxins collect mainly on the ____ side of plants
Darker
how do auxins behave in stems?
- Stimulate cell expansion
- Stimulate cell elongation
Darker side will grow faster. Results in stem bending towards the light source.
What is geotropism?
Growth response of a plant towards gravity
Why does a root grow straight down?
Auxins collect on the side-tip of the root and move upwards evenly
What is the effect of auxins in roots?
- Inhibits cell elongation
Therefore, the cells on the upper side of the root grow faster than the cells on the lower side of the root.
This makes the root grow TOWARDS gravity
What is negative geotropism?
The upward growth of plant parts (growth against the force of gravity)
What is positive geotropism?
The downward growth of plant parts. (this is growth towards the force of gravity)
What are plant defence mechanisms?
Adaptations that have evolved in plants.
These adaptations improve their survival and reproduction rates by reducing the impact of herbivores.
What are types of defence mechanisms used by plants?
- chemical defences
- mechanical defences
- mimicry
How can defensive chemicals be grouped into classes?
Based on their structures and how the plant makes them.
Name some actions that function as the plants’ chemical defence mechanism
- Interference with neurotransmitters
- Addictive
- Caffeine (coffee)
- Morphine (poppy)
- Nicotine (tobacco)
- Addictive
- Odours
- attract predators or parasites
- kill damaging herbivore
- Certain animal enzymes react with these compounds (poisonous)
- attract predators or parasites
- Distateful and toxic secretions
What are mechamical defences
external defences that discourage animals from feeding on them
How can a plant’s stem or leaves be mechanially adapted?
They could have sharp prickles, spines or thorns.
These reduce feeding by a large group of ungulate herbivores.
Feeding is reduced by:
- Restricting feeding rate
- Wearing down molars
Give one mechanical adaptation that can occur in some plant tissues?
- Sharp toxic needles can occur in plant tissue
- makes ingestion painful
- damages mouth and gullet
- enables plant’s toxins to enter bloodstream more easily
What does “ungulate” refer to?
A large group of mammals that have hooves
How can the structure of a plant be adapted to reduce herbivore impact?
- Branching and leaf arrangement
- Eg. Acacias have long spine in the part of the canopy but short spines in the part of the canopy where the giraffes cannot reach
What are adventituous roots?
Roots that arise from an organ other than roots
What are the two main components of vascular tissue?
Xylem and ploem
What is apical dominance?
When the main central stem grows more strongly than others.
What does “differentiation” refer to?
When distrinct cell types arise from other cells
What can the stem also be called?
Petiole
What is an abscission layer?
A layer that blocks off the supply of carbohydrates to the leaves
What is leaf senescence?
Recycling of nutrients
What is seed dormancy?
When seeds are prevented from germinating
What is stomatal closure?
The closure of stoma (pores) on the underside of a leaf
This reduces water loss via transpiration
What is a meristem?
Region of plant tissue found chiefly at the growing tips of plant roots and shoots
What is a biennial plant?
A plant that lives for two years
What does a hydrolytic enzyme do?
Catalyses the chemical bond making proteins, nucleic acids, starch, fats, phosphate esters, and other macromolecular substances.
What is a monoecious plant?
Plants that contain both male and female flowers
