Plant Biology Flashcards
(In Root) Epidermis
Outermost layer of cells. Provides stem protection from external environment and controls gas exchange.
Cortex
A thick layer of packing cells. Stores food, supports plant, and synthesizes secondary metabolites.
Xylem
(Star Shaped in Root) (Inside the Pith) Transports water and minerals.
Phloem
(Circle Surrounding Star) ( Outside the Pith) Transports sucrose and amino acids.
(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.
Cuticle
Waxy substance used to prevent leaf losing water and drying out.
Palisade Mesophyll
Tightly packed cells below the epidermis that have lots of chloroplasts. The site of the most photosynthesis.
Spongy Mesophyll
Contains fewer chloroplasts and has air spaces to allow for gases to circulate.
Stomata
Tiny pores that are responsible for gas exchange and transpiration
Guard Cells
Control the opening and closing of Stomata to regulate how much gas leaves and enters the leaf.
When do Stomata Open
During the Day
Water passes into the guard cells by osmosis, thus making them bend to open the stoma.
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
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.
Stomatal Density
How many stomata are present on a specific leaf area.
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.
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.
Lignin
Provides the xylem wall strength and reduces tension to prevent collapsing.
Pits
Allows movement of water outside of the xylem into the phloem.
Dead Cells and Loss of End Walls
Allows easy movement of continuous column of water.
What is Transpiration
The loss of water vapour from the stems and leaves of plants through the stomata.
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.
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.
Significance of Transpiration for Plants
Provides water for photosynthesis.
Transports mineral ions.
Cools the leaf as water evaporates.
Translocation
Transportation of sucrose and amino acids in both directions from source to sink.
