Transport in plants

Why do multicellular plants need transport systems

Why do multicellular plants need transport systems

Metabolic demands, size and surface area to volume ratio

Metabolic demands

Nutrients obtain in one part of the plant need to be transported to other cells.

Surface area : volume ratio

Multicellular plants have a small SA:V ratio so they can’t rely on diffusion alone for transport.

Vascular system structure in the stem

Vascular bundles are found around the edge to give strength and support.

Vascular system structure in the roots

Vascular bundles are in the middle to help the plant withstand tugging strains.

Vascular system structure in dicot leaves

The midrib is the main vein carrying the vascular tissue and helps to support the structure of the leaf.

Xylem is always

Inside the phloem

Structure of xylem vessels

Long, hollow structures made by several columns of cells fusing together.

Xylem parenchyma

Thick walled cells pack around the xylem vessels, storing food and containing tannin deposits (chemical protection from predators).

Xylem fibres

Long cells with lignified secondary walls that provide extra mechanical strength.

Phloem structure

Living tissue with no organelles, containing phloem sap that transports organic solutes around the plant (up and down).

Sieve tube elements

The main transporting vessels of the phloem

Sieve plates

In the areas between cells, the walls become perforated to form sieve plates

Companion cells

Linked with sieve tube elements by plasmodesmata to perform cell functions.

Meristematic tissue

It is located between the the phloem and xylem tissues and produces stem cells for vascular growth.

Palisade cell specialisation

Contain many chloroplasts, rectangular, thin cell walls, large vacuole

Root hair cell specialisation

Increase surface area of the cell, thin cell wall, vacuole containing ions and sugars

Guard cell specialisation

Thick inner cell wall

Ribosomes

The site of protein synthesis

Rough endoplasmic reticulum

A network of membranes attached to the SER with ribosomes bound to the surface. It is responsible for the synthesis and transport of proteins.

Smooth endoplasmic reticulum

A network of membranes attached to the nucleus, not containing ribosomes. It is responsible for lipid and carbohydrates synthesis and storage.

Golgi apparatus

A structure formed of cisternae which puts proteins into vesicles (lysosomes or secretory)

Lysosome

A specialised vesicle that contains digestive enzymes to break down waste materials.

Mitochondria

Contain a double membrane with the inner membrane folded and containing enzymes to perform aerobic respiration.

Chloroplasts

They have a double membrane with the inner membrane forming a granum which contains chlorophyll for photosynthesis.

Vacuole

Membrane lines sacs containing cell sap to maintain cell turgor.

Peroxisome

Contains enzymes to break down hydrogen peroxide (protection against bacteria).

Nuclear envelope

A double membrane containing the DNA in the nucleus.

Magnification

The number of times bigger an image is than the actual object.

Resolution

The ability to distinguish between two points that are close together.

What is the difference in resolution between light and electron microscopes?

Electron microscopes have a higher resolution, as they used beams of electrons with short wavelengths. This makes it easier to distinguish between different structures.

Light microscopes (8)

Inexpensive, small, simple sample prep, no vacuum, colour, up to 2000x magnification, resolving power is 200nm, samples can be living

Transmission electron microscope

The beam is transmitted through the specimen - best resolution

Scanning electron microscope

The beam is sent across the surface and reflected electrons are collected - resolution is worse

Hydrogen bonding

Polar molecules (water) interact with each other as the positive and negative regions attract each other and form weak bonds.

High boiling point of water

It provides a constant environment for aquatic animals

Solid water is less dense than liquid

Ice floats, forming an insulating layer so that habitats don’t freeze.

Waters cohesive/adhesive properties

It is an efficient transport medium within living things because molecules stick together.

Water acts as a solvent

It is polar so can carry polar molecules dissolved in it and acts as a medium for chemical reactions (cytosol).

Water acts as a coolant

Maintains constant temperatures in cellular environments for enzyme activity.

Water absorption

Roots absorb water from the soil through root hairs with a high water potential by osmosis.

Movement up the stem

Water travels up the stem through xylem vessels by capillary action

Transpiration pull

As water evaporates from the leaves, it creates a suction force that pulls more water up the xylem.

Evaporation

Water reaches the leaves, where it evaporates from a mesophyll cell travels through air spaces and out of the stomata.

Apoplastic pathway

Water moves through cell walls and the spaces between cells - stops at the casparian strip.

Symplastic pathway

Water moves through the cytoplasm of cells through plasmodesmata.

Light as a limiting factor

Increasing light intensity gives increasing numbers of open stomata, increasing the rate of water vapour diffusing out.

Relative humidity as a limiting factor

A high relative humidity will lower the rate of transpiration because of the reduced water vapour potential gradient between the leaf and air.

Temperature as a limiting factor

Increase in kinetic energy of water molecules, increases rate of evaporation.

Air movement as a limiting factor

Wind increases the rate of transpiration because water vapour potential around stomata decreases, increasing diffusion gradient.

Soil-water availability

If it is very dry the plant will be under water stress so will close its stomata and the rate of transpiration will decrease.

Hydrophytes

Plants with adaptations that enable them to survive in wet habitats.

Xerophytes

Plants with adaptations that enable them to survive in dry habitats.

Hydrophyte adaptations (5)

Thin waxy cuticle, open stomata, wide flat leaves, small roots, air sacs

Xerophyte adaptations (5)

Thick waxy cuticle, sunken stomata/hairs, reduced stomata, long/wide roots, curled leaves (marram)