Unit 9 Plants Flashcards
What are the layers of tissue in the stem and roots of plants
Stem
Outer coating is called epidermis
Intermedia later is called cortex
The inner layer is the pith
The cambium is a thin layer diving the cortex and the pith, they have vascular bundles which are composed of both the xylem and the phloem
Root
Epidermis and cortex are the same
Has root hair that are like projections
Innermost tissue layer is called the stele lined by the epidermis.
In the center the xylem is cross shaped and the phloem fills in the rest of the hole.
Outline the structure of the phloem + adaptations
Long continuous tube of live cells called sieve tube cells, separated by sieve plates.
Each tube cells has companion cells which carry out metabolic functions.
Movement through the phloem is called translocation, can occur in both directions. However genuinely goes from sources (leaves and stem, high solute concentration) to sinks (areas with low solute concentration, fruits, or developing roots)
Adaptations
Contain many mitochondria for active transport of sucrose
Rigid cell walls withstand pressure gradient
Outline how the phloem translocates sucrose all throughout the phloem
Phloem loading
Apoplastic
1. Sucrose is in a source.
2. H+ ions are actively transported from companion cell into source, which creates a concentration gradient
3. H+ ions diffuse back down with co transporter protein, providing energy for sucrose to be transported into sieve tube cells.
Symplastic
Or else sucrose can also simply diffuse via small gaps (plasmodesmata) into companion cells where it is converted into another molecule before entering the phloem so it the concentration gradient is maintained.
Translocation
Movement of sucrose due to changes in pressure
High conc. of sucrose at source, water is drawn into phloem from the xylem via osmosis
Builds hydrostatic pressure in the phloem and forces sap to move from the source to a lower pressure area (sink).
Sucrose is withdrawn into sink from phloem decreasing osmotic pressure, allowing water to diffuse back into xylem decreasing hydrostatic pressure
Outline the structure of the xylem and function and how water is transported
Long continuous tube of dead hollow cells. Cell wall contains pits (pores) enabling water to be transferred between cells
Walls have thickened cellulose and are reinforced by lignin to provide strength
Transports water (one direction) and mineral ions
Relies on passive movement of water established due to cohesion between water molecules and adhesions between the water molecules and the hydrophilic xylem wall.
Allows water to be pulled through xylem in a continuous stream.
- Water evaporates through levels it creates low pressure in leafs, adhesion draws water into the leaf, lowering the pressure in the xylem, which causes water to be drawn up from the roots.
Known as transpiration pull
How does water enter the roots
Mineral ions move through soil by diffusion until they come in contact with root hair cell
Protein pumps actively transport them into root cells, establishing a concentration gradient, allowing water to diffuse into the root via osmosis.
What is responsible for indeterminate growth in plants and how is growth regulated
Apical meristem on tip of root and shoot
These structures can divide mitotically where 1 pluripotent cell will remain in the meristem to divide once more, the other will differentiate into a specific tissue. Allows the retention of pluripotency in plants.
Auxin hormone
Regulate growth, leaf development and flower formation
Aims to promote cell elongation when stimulated by the apical meristem, also inhibits auxiliary buds left behind by the apical meristem. This is known as apical dominance.prevents the lateral growth of plants (widenning of plants, or the branching of plants, unless the tip of the shoot is cut off)
Outline the two types of tropism
Phototropism= growth in response to light (positive tropism: shoots grow towards light, negative phototropism: roots grow away from light)
How?
1. Protein called phototropism, found in tip of a shoot and changes conformation in response to light
2. Allows it to bind to regulators of gene expression causing the production of P1N3 proteins
3. These proteins trigger auxin pumps to move auxins to the shaded side of the shoot
4. There auxin binds to auxin receptors , causing a change in gene expression
5. H+ ions are secreted weakening the bonds in the cell wall, allowing the cell to elongate
6. Causes the shaded side to bend so plants faces the light.
Gravitropism (shoots grow away from gravity (negative gravitropism, shoots grow towards gravity (positive))
1. Molecules called statoliths accumulate on lower side of a root
2. Auxin is transported to root tip
3. Higher concentration of auxin inhibits upward growth, bending the roots downwards towards gravity.
Explain how flowering occurs in short and long day plants
Short day plants
- flower when days are short, so when its dark for longer than a specific threshold
Long day plants
- flower when days are long, when its dark for less than a specific threshold
Occurs when light is absorbed by a pigment called phytochrome
Inactive Pr
- absorbs light of 660 nm to become activated Pfr
Activated Pfr
- absorbs light of 730 nm to become inactivated Pr
Sunlight has more than 660 nm so in daylight Pfr accumulates, however Pr is more stable than Pfr, nighttime reduces levels of Pfr.
So Pfr stimulates flowering in long day plants as:
- it triggers transcription of FT mRNA which is transported to the apical meristem and translated into proteins responsible for flowering
However Pfr inhibits flowering in short day plants.
Define pollination and seed dispersal
Pollination
Transfer of pollen grains from an ather (male) to a stigma (female)
improves genetic diversity
Some plants contain both and can self pollinate
Seed dispersal:
Fertilization results in seed and it moves away from parent plant
This reduces competition for resources between seed and parental plant
List mechanisms of seed dispersal
wind, water, fruits, and animals
Define mutualism + example
Pollinators are involved in a mutualistic relationship with the flowering plant - both species benefit from interaction
Bees fly from flower to flower to gather nectar - they make it into food, benefiting the bees.
When they land in a flower, they get pollen on them, and when they land on another, some pollen rubs off, pollinating the plant - benefiting plants.
Draw and label structure of seed + function of different parts
Epicotyl = embryonic shoot, plumule
Radicle = embryonic root
Micropyl = hole through which water enters
Testa = seed coat, protects
Cotyledon = contains food stores
See notion
Draw and label both a male and female flower
Male part (stamen): anther (pollen producing) + filament (supporting anther, makes accessible to pollinators)
Female part (pistil): stigma (sticky tip of pistil responsible for catching pollen), style (tube shaped connection between stigma and ovule, elevates stigma), ovule (structure that contains female reproductive cells
Petals - attract pollinators
Sepal - protects flower when in bud
Peduncle - stalk of flower
See notion
Define germination and what is required for it to occur
Process by which a seed emerged from a period of dormancy and begins to sprout
- absorption of water, which causes gibberellin to be produced
- Gibberellin triggers the synthesis of amylase, which breaks down starch into maltose
- Maltose is either hydrolysed (to glucose) for energy, or polymerised (to cellulose) for cell wall formation
This energy and cellular building blocks is used to promote cell division and the growth of a nascent shoot
Then
The testa ruptures and the radicle grows into the ground to extract key nutrients and minerals
The cotyledon emerges and produces the growing shoot’s first leaves
Oxygen – for aerobic respiration (the seed requires large amounts of ATP in order to develop)
Water – to metabolically activate the seed (triggers the synthesis of gibberellin)
Temperature – seeds require certain temperature conditions in order to sprout (for optimal function of enzymes)
pH – seeds require a suitable soil pH in order to sprout (for optimal function of enzymes)
Define xerophyte and halophytic + give adaptations
Xerophytes: can tolerate dry conditions (eg desert plants)
Reduced leaves - reduce surface area for water loss
Rolled leaves - reduces exposure of stomata and evaporation rate
Thick, waxy cuticle
Halophytes: tolerate salty conditions (eg marshlands)
Salt excretion - certain part of the plant contains salt glands that actively eliminate salt
Root level exclusion - roots structured to exclude up to 95% of salt in soil solutions
