Plant Biology Flashcards
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
Where are Meristems Found
On the tip and along the length of a branch or stem.
Seed Structure
Testa: Seed coat
Cotyledon: Storage for food
Radicle: Embryonic Root
Plumule: Embryonic Shoot
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.
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.
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.
Pits
Allows movement of water outside of the xylem into the phloem.
Palisade Mesophyll
Tightly packed cells below the epidermis that have lots of chloroplasts. The site of the most photosynthesis.
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.
What is Transpiration
The loss of water vapour from the stems and leaves of plants through the stomata.
Stomata
Tiny pores that are responsible for gas exchange and transpiration
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.
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.
Tropism
The growth of the plant in response to environmental stimuli.
Auxin Efflux Carriers
Also known as PIN3 proteins, they actively pump auxin out of the cell. They are activated by sunlight.
Xylem
(Star Shaped in Root) (Inside the Pith) Transports water and minerals.
Significance of Transpiration for Plants
Provides water for photosynthesis.
Transports mineral ions.
Cools the leaf as water evaporates.
Cortex
A thick layer of packing cells. Stores food, supports plant, and synthesizes secondary metabolites.
(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.
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.
Features of the Stamen
Anther: Contains pollen, a powdery substance with male nuclei inside for reproduction.
Filament: Structurally supports the anther.
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.
Function of Companion Cell
Provide metabolic support for sieve tube element and facilitate loading and unloading in source and sink.
Guard Cells
Control the opening and closing of Stomata to regulate how much gas leaves and enters the leaf.