VCE BIOLOGY UNIT ONEChapter Four

Plants

Dr Adrian Mascia

Plant Structure

Plants can be divided into 2 systems

1. The Shoot system (above ground) – stem, leaves, reproductive organs

2. The Root system (below the ground) – roots and root hairs

Inputs and outputs

Plant Tissues

• There are 4 main types of plant tissues1. Meristematic Tissues (tissue undergoing mitosis)

2. Dermal tissue (Outer layer)

3. Vascular Tissue (Tissues responsible for transport of water and nutrients)

4. Ground Tissue (All internal cells other than vascular tissue)

Meristematic tissue

•Meristematic tissue is composed of cells undergoing Mitosis

•These cells are found at the tips of roots and shoots in a plant and in a ring around the inside of stems and branches

•Meristems are the only places that growth occurs in a plant

•Some meristem cells differentiate after divison and make up the other 3 primary tissues

Dermal Tissue

• Outer most layer of the plant

• Acts as a skin preventing abrasion, invasion from other organisms and controlling water loss

• On leaves and stems usually produce a waxy cuticle to prevent water loss

Ground Tissue

• Consist of a variety of cells

• Functions include storage, support and photosynthesis

• Examples include fleshy portions of apples, pears, potatoes

Vascular Tissues

• Transport tissues including xylem and phloem

• Xylem = Water transport

• Phloem = Nutrient transport

• Circulatory system of the plant

Xylem

• Xylem is water conducting tissue that carries water from the roots to the rest of the plant

• When the cells mature, they die, leaving behind hollow cells

• In some flowering plants xylem vessels have open ends and are arranged end to end forming long continuous tubes

• Wood is composed entirely of xylem tissue and provides the main support for most large plants

• (Figure 4.11, Nelson, Pg 89)

Phloem

• Unlike Xylem cells, mature phloem cells are living

• Form sieve tubes (long thin cells with large pores arranging themselves end to end)

• Used for the transport of sugars from the roots to the tips of the plant

• (figure 4.11, Nelson, Pg 89)

Interactions between Xylem and Phloem

• Sucrose moves into the sieve cells, causing water to move across from the xylem to the Phloem via osmosis

• Sieve cells a re controlled by companion cells as they have no nucleus or mitochondria

ROOTS2 Types of roots

1. Tap roots: Large tapering main root with only slender, short side branches. Capable of burrowing very deep into the ground e.g. Eucalypts, daisies, orchids

2. Fibrous roots: Many small roots of about equal size, do not grow deeply, rather spread out e.g. Grasses

Purpose of roots

• Anchorage

• Provide large surface area to collect water and nutrients from the soil (presence of root hairs greatly increases this surface area (by up to 130 times)

Root Hairs

• Root hairs penetrate between soil particles, coming in close contact with the soil water

• Water from the soil is able to pass from the soil through the plasma membrane of the root hair through osmosis

• Minerals enter through the plasma membrane through diffusion and active transport

Root Pressure• How does the water

make its way all the way to the top of the tree?

• As the water is taken in by the roots it moves into the xylem. As the thin tubes of the xylem fills, that water column within the plant goes higher and higher

• The thin yet strong structure of the tubules in the xylem allow a ‘water columns’ or transpiration streams to form

Leaf Structure

• Location / shape / orientation are all designed to take in maximum amount of sunlight

• (large surface area to volume ratio, at the top of the plant, lean towards the sun)

INTERNAL LEAF STRUCTURE• Cuticle: waxy covering which is

impermeable to water. Prevents water loss through evaporation

• Upper Epidermal layer: several stomata pores present in this layer. Protective function

• Palisade cells: Type of chloroplast, elongated cells directly beneath the epidermis, collectively called the palisade mesophyll (site of photosynthesis)

• Spongy mesophyll: Fills the leaf from the palisades down to the lower epidermis, contains large amounts of free space which can be used for water storage, some chlorophyll present (usually moisture saturated)

Large amount of space within the mesophyll means that there are large areas of cell walls exposed for diffusion

• Stomata: Small opening through the epidermis and cuticle

Allows the diffusion of CO2 into photo synthetic tissue

Xylem and phloem

Stomata & Guard Cells• Guard cells: border the stomata. When they

swell with water the stomata opening becomes exposed, when low in water they constrict closing the stomata opening

• A greater number of stomata are found on the underside of a leaf as this prevents exposure to sunlight, thus lowering water loss.

Special ways of obtaining nutrients in plants

• As spoken about earlier, most plants actively transport minerals into their systems through the root hairs, however some soils are mineral deficient, so plants have adapted other means of getting these nutrients.

• Nitrogen Fixing Bacteria can often work in a relationship with plants, The plant provides a home for the bacteria, whilst the waste product of the bacteria (nitrogen) is supplied to the plant

• Plants living in Humus rich soil have developed an association with a fungus, causing increased surface area to absorb nutrients

• Others have the ability to break down Humus into soluble nutrients, some of which can be used by the plant.

• Other plants are Carnivorous and devour insects as a means of obtaining vital nutrients not supplied by soil

Distributing energy around a plant• Energy made from photosynthesis is

stored as sugars. These sugars need to be distributed from the leaves where it is made, to the rest of the plant.

• This process is called Translocation

• Sugars are actively pumped (energy comes from mitochondria in companion cells) from their storage site into the phloem, causing water from the xylem to move via Osmosis into the phloem.

• This creates a sugary solution that can travel around the plant via the phloem to areas which require energy

Removing Waste in plants

• There are several methods plants use to dispose of waste

• Transported to the leaves or bark, which are then dropped off, removing the substance from the plant

• Store as crystals or dissolved in the vacuoles.• Store in non living tissue• Exude resins, fats, waxes- e.g. latex from

rubber tree (Other substances include excess salt, gases, etc)

Single Cell Organisms

- Have the same requirements for life as multicellular organisms, their structure creates a difference in the method of obtaining these essentials

Requirements:1. Nutrients for construction and structure 2. Energy to replenish and repair

Obtaining essentials

MINERALS / WATER

Single cell organisms utilise diffusion and osmosis in order to in take essential substances such as Gases for respiration, and water.

ENERGY

Autotrophs: Take energy from the non living world

(Photosynthesis, Chemosynthesis) e.g. Diatoms

Heterotrophs: Take energy from the living world (Ingestion through the cell membrane / Breaking down of other small organisms) e.g. Paramecium

LOCOMOTION

As single celled organisms do not have the ability to for tissues that work together to generate leverage, they have other ways of propelling themselves

Flagella : whip like tail

Cilia: small hairs

Eating

As mentioned, some single celled organisms rely on the diffusion of all energy and minerals to diffuse through their plasma membrane

Other organisms such as the Paramecium use their cilia to sweep organisms into their oral groove, so it can then be digested in the gullet

Organisation

Some single celled organisms, particularly bacteria will form colonies. They are still individual organisms, however their close proximity allows them to share resources.