Plant Biology Flashcards
Stomatal Density
How many stomata are present on a specific leaf area.
Sink
The site where solutes are unloaded from the phloem.
Plant Meristem
A group of undifferentiated cells that retain the ability to divide by mitosis and differentiate to all types of cells allowing growth.
Auxin and Shoot Response to Light
If a shoot is exposed to light, more auxins move in the shaded side.
Auxins cause cells in the dark to grow faster.
This causes an imbalance in both sides which makes the shoot bend towards sunlight.
Process of Transpiration
Water moves up from the roots to the leaves through the xylem. In the leaves, water evaporates into the air through the stomata. This creates a suction force, pulling more water up from the roots. Water molecules stick together and to the xylem walls through cohesion and adhesion, creating a continuous column. Lignin in the xylem walls prevents them from collapsing and resists tension. This lowers the water potential in the roots, causing water to diffuse from the soil into the roots.
(In Leaf) Epidermis
Thin layer of protective cells covering the leaf. Transparent so no light can pass through, and has no chloroplasts. Produces waxy cuticle.
Lignin
Provides the xylem wall strength and reduces tension to prevent collapsing.
Auxin Efflux Carriers
Also known as PIN3 proteins, they actively pump auxin out of the cell. They are activated by sunlight.
When do Stomata Close
During the Night
Water passes out of the guard cells by osmosis, thus straightening them and closing the stomata pores.
Hot and Dry Weather
Stomata close to help prevent the plant from wilting
Stomata
Tiny pores that are responsible for gas exchange and transpiration
When do Stomata Open
During the Day
Water passes into the guard cells by osmosis, thus making them bend to open the stoma.
Difference with Self and Cross Pollination
Self Pollination is when the flower uses the same pollen on the same plant.
Cross Pollination is when the flower uses pollen on a different plant but the same species.
Features of the Pistil
Stigma: The sticky surface at the top of the pistil used for pollen to stick.
Style: An elevator for the stigma to the ovary.
Ovary: Contains ovules which later develops into seeds upon fertilization.
What is Transpiration
The loss of water vapour from the stems and leaves of plants through the stomata.
The 5 Major Phytohormones
Auxin: Promotes stem elongation and root development.
Cytokinin: Stimulates cell division and differentiation.
Gibberellin: Promotes stem elongation and seed germination.
Ethylene: Involved in fruit ripening.
ABA: Promotes seed dormancy.
Steps for Reliable Data for Stomatal Density
Repeat measurements and take an average.
Analyze stomatal density across various parts of the leaf and different leaves.
Process of Unloading Sucrose
In the roots (sink), the sucrose is actively unloaded from the phloem into the respiring cells
This raises the water potential and lowers solute concentration in sieve tubes.
At the same time, ions are being pumped into the xylem from the soil into the roots by active transport, thus reducing water potential in the xylem.
Water diffuses by osmosis from the sieve tube into the xylem. This ensures that the hydrostatic pressure at the sink is always lower than the pressure at the source. Hence, phloem sap will always move from source towards the sink.
Process of Loading Sucrose
At the source, sucrose produced from photosynthesis by the mesophyll cells in the leaf is loaded into the phloem companion cells by active transport.
Sucrose then moves into the sieve tube element through diffusion along the plasmodesmata
This increases solute concentration in the phloem, thus water from xylem diffuses into sieve tubes through osmosis
This increases water potential, so the water and dissolved solutes are forced downwards towards the sink to relieve pressure
Features of the Stamen
Anther: Contains pollen, a powdery substance with male nuclei inside for reproduction.
Filament: Structurally supports the anther.
Features of Sieve Tube Element
Long and narrow living cells that are connected together.
Have end walls which have many pores (forming sieve plates) to allow sap to flow between cells.
Have no nuclei and few organelles to maximize space for translocation.
Have thick and rigid cell walls to withstand the hydrostatic pressure.
Cuticle
Waxy substance used to prevent leaf losing water and drying out.
Adaptations of the Leaf for Gas Exchange
Flat: Provides large S.A for more gas exchange.
Thin: Provides short diffusion distance for easier gas exchange.
Moist Inner Environment: Moisture helps maintain humidity in the leaf which is important for CO2 diffusion.
Methods of Seed Dispersal
Wind
Animal Wastes
Animal Fur
Burrowing Animals
Seed Germination
The process where the dormant seed undergoes growth and development and emerges into a seedling.
Guard Cells
Control the opening and closing of Stomata to regulate how much gas leaves and enters the leaf.
Importance of Stomatal Density in Plant Functions
Stomata control how much CO2 enter and leaves the leaf for photosynthesis.
Stomata control water vapor release through transpiration.
Tropism
The growth of the plant in response to environmental stimuli.
Pits
Allows movement of water outside of the xylem into the phloem.
Function of Companion Cell
Provide metabolic support for sieve tube element and facilitate loading and unloading in source and sink.
Dead Cells and Loss of End Walls
Allows easy movement of continuous column of water.
Significance of Transpiration for Plants
Provides water for photosynthesis.
Transports mineral ions.
Cools the leaf as water evaporates.
Advantage and Disadvantage of Self Pollination
Advantage:
Good strain will produce more good strains
Disadvantage:
Lack of diversity will result in lower vigor in offspring (weakness)
Advantage and Disadvantage of Cross Pollination
Advantage:
Diversity will result in more adaptation to environment changes (Enhanced Vigor)
Disadvantage:
Good strains will worsen over generations
Factors that Affect Rate of Transpiration
Humidity: As humidity increases, the transpiration decreases as the diffusion gradient is reduced.
Temperature: As temperature increases, transpiration increases as molecules move faster and evaporate faster.
Light Intensity: When light intensity is high, the stomata will open to let CO2 in for photosynthesis, this allows water vapor to leave easily.
Wind Speed: As wind speed increases, more water vapor is lost because the wind is carrying it which leads to higher rate of transpiration.
Source
The site where solutes are loaded into the phloem.
The 5 Processes of Plant Reproduction
Meiosis
Pollination
Fertilization
Seed Dispersal
Seed Germination
Features of Companion Cell
Small cells with large nuclei and dense cytoplasm found adjacent to the sieve tubes.
Contain many mitochondria to produce ATP for loading into sieve tubes.
Contain transport proteins to load and unload materials for the sieve tube.
Ethylene Ripening in Fruits
When a fruit ripens, ethylene gas is produced.
Ethylene molecules bind to the receptors in the fruit cells.
The binding to the fruit cells triggers changes in gene expression which lead to ripening.
Ripening includes change of color and softening of fruit flesh.
This ethylene gas stimulates adjacent fruits to also ripen, which causes a loop until ripening is complete.
After Fertilization, What Happens?
The 4 components of the plant dry up and fall.
The ovule develops into a seed.
The ovary wall enlarges and becomes the fruit.
Process of Cell Growth using Auxin
Auxin is produced in all cells as soon as shoot is exposed to light.
Auxin efflux pumps auxin out of cells from the light side into the dark side.
This causes auxin to bind to receptor proteins on the cell surface membrane.
ATPase proton pumps start pumping H+ across the cell surface membrane, thus lowering the pH of the fluid filled spaces of the cell wall.
The low pH causes enzymes named expansins to get activated which loosen linkages between microfibrils and polysaccharides which makes the cell wall loose.
This results in potassium (K+) to get pumped into the cytoplasm, therefore lowering water potential in the cytoplasm.
Water then enters the cytoplasm through osmosis and makes the cell expand without losing overall wall strength.
This expansion along with the other cells causes the dark side of the shoot to grow faster than the brighter side, thus making the shoot move to the light side.
Spongy Mesophyll
Contains fewer chloroplasts and has air spaces to allow for gases to circulate.
Where are Meristems Found
On the tip and along the length of a branch or stem.
Methods of Promoting Cross-Pollination
Differential Maturation Times
Separate Flowers or Plants
Animals
Wind
Xylem
(Star Shaped in Root) (Inside the Pith) Transports water and minerals.
Organs in the Flower
Petals: Colorful parts of the flower which attract insects for pollination.
Sepals: Leaf-like structures that protect the developing flower.
Pistils: The female reproductive organ of the flower.
Stamens: The male reproductive organ of the flower.
(In Root) Epidermis
Outermost layer of cells. Provides stem protection from external environment and controls gas exchange.
Process of Seed Germination
Water is absorbed, thus stimulating the production of Gibberellin hormone.
Gibberellin triggers the production of an amylase enzyme.
Amylase digests the starch stored in the seed into sugars.
The sugars produced are used as an energy source for the embryo.
The radicle grows first to fix the seedling into the soil where it can absorb water.
The shoot grows vertically.
The seed is now a seedling.
Once the shoot grows a leaf, the seedling becomes fully independent and doesn’t need to rely on storage materials.
The plant can now photosynthesize and make its own food.
Xylem VS Phloem
Xylem has Dead Cells
Phloem has Alive Cells
Xylem has no end wall in between
Phloem has end walls in between
Xylem moves upwards only
Phloem moves upwards and downwards
Xylem transports water and minerals
Phloem transports sucrose and amino acids
Xylem has a thick wall
Phloem has a thin wall
Cortex
A thick layer of packing cells. Stores food, supports plant, and synthesizes secondary metabolites.
Function of Sieve Tube Element
Loading, transporting, and unloading of sucrose and amino acids.
Palisade Mesophyll
Tightly packed cells below the epidermis that have lots of chloroplasts. The site of the most photosynthesis.
Transpiration VS Translocation
Transpiration is the movement of water and minerals from soil to leaves
Translocation is the movement of sucrose and amino acids from source to sink
Transpiration is passive
Translocation is active
Process of Fertilization
The pollen grain falls on the stigma, which produces a sticky fluid.
The pollen grain absorbs the liquid and makes a pollen tube.
The pollen tube produces enzymes that digest the tissue of the style, digging down until they reach the micropyle: a gap in the covering of an ovule where male gametes enter.
The pollen tube delivers two male nuclei.
The first nucleus fuses with the egg to produce a zygote, while the other nucleus combines with two polar nuclei in the ovule to produce endosperm. The endosperm provides nutrients for the plant in seed germination.
Phytohormones
Chemical messengers that play a crucial role in regulating plant growth, development, and responses to stimuli.
Advantages of Positive Phototropism
More insects can find flowers for pollination.
Plant gets higher for better seed dispersal.
Leaves are exposed to light for more photosynthesis.
Importance of Seed Dispersal
To make sure that the seed has enough water, space, and nutrients as well as to prevent competition with its own offspring and overcrowding.
Requirements for Seed Germination
Water: To rehydrate the seed and activate enzymes
Oxygen: Respiration
Warm Temperature: To provide optimum temperature for enzymes to catalyze reactions
Phloem
(Circle Surrounding Star) ( Outside the Pith) Transports sucrose and amino acids.
Auxin and Cytokinin in Shoot and Root Growth
Auxin promotes shoot growth and inhibits root growth.
Cytokinin promotes root growth and inhibits shoot growth.
Auxin travels downwards towards the root.
Cytokinin travels upwards towards the shoot.
Difference with Positive and Negative Tropisms
Positive tropisms move towards the stimulus.
Negative tropisms move away from the stimulus.
Translocation
Transportation of sucrose and amino acids in both directions from source to sink.
Seed Structure
Testa: Seed coat
Cotyledon: Storage for food
Radicle: Embryonic Root
Plumule: Embryonic Shoot
