Unit 2.5 Plant Transport Flashcards
Flowers
The reproductive organs of plants.
Once the flower is pollinated, the ovule is fertilised and becomes a seed.
The ovary wall becomes a fruit for seed dispersal.
Plant organs involved in transport
Leaves
Stem
Roots
Leaf structure
Leaves are the main site of photosynthesis in a plant.
The tissues seen in cross section are the upper epidermis (covered with a waxy cuticle), palisade mesophyll, spongy mesophyll and lower epidermis (containing stomata surrounded by guard cells).
Stomata
Tiny holes on the underside of leaves.
Surrounded by 2 guard cells which control the opening and closing of each stoma.
Stomata allow gas exchange between the leaf and its environment.
Water can escape through open stomata (transpiration).
Substances transported by plants
Carbon dioxide and water (for photosynthesis)
Oxygen (waste product of photosynthesis, required for respiration)
Sugars (products of photosynthesis)
Minerals such as nitrates (used to make other chemicals, eg. amino acids).
Root hair cells
Used to absorb water containing dissolved minerals from the soil into the root.
They have a large surface area for absorption.
Xylem
Specialised tissue for transporting water up the stem of plants.
Made of dead cells with no cell contents, joined end to end to form strong tubes.
The cell walls contain rings or spirals of lignin, which kills the cell and strengthens it so that it won’t collapse.
Wood is made of xylem.
Transpiration Summary
The process by which water moves through a plant and exits through the leaves.
Water enters through the root hair cells, crosses the root, moves up through the xylem, across the leaf and out through the stomata.
Osmosis
Movement of water across a selectively permeable membrane from an area of high to low water concentration.
Water is pulled across the leaf and root by osmosis between cells.
Transpiration in detail
Water evaporates from air spaces in the leaf and exits through open stomata.
More water evaporates from mesophyll cells to replace it.
Water is pulled from cell to cell across the leaf by osmosis, and is then pulled from the xylem.
Water moves up the xylem as a column, which pulls water across the root from cell to cell by osmosis.
Water is pulled in from the soil via root hair cells.
Importance of transpiration
Carries water to the leaves for use in photosynthesis.
Transports minerals, dissolved in soil water.
Cools leaves by evaporation.
Part of the water cycle, moving water from soil to atmosphere.
Factors affecting the rate of transpiration
Temperature
Wind speed
Humidity
Leaf surface area
Rate of photosynthesis
Bubble potometer
Sealed glass apparatus used for measuring the rate of transpiration in a shoot.
Must be filled underwater to prevent air bubbles in the xylem.
The rate of movement of an introduced air bubble can be measured in different conditions.
Weight potometer
A plant in a pot or a container of water is placed on a balance and weighed.
The decrease in mass over time can be used to estimate the rate of transpiration.
The plant pot must be placed in a bag and sealed around the stem, or oil must be floated on the water to prevent evaporation from the surface.
Phloem
Specialised tissue for the transport of sugars (translocation) in plants, both up and down stems.
It is a living tissue made of 2 types of cells - sieve tubes and companion cells.
