PLANT TISSUES <ul><li>Plant tissue can be divided into three major types: </li></ul><ul><li>Vascular plants tend to have specialised sections which perform specific tasks. This results in the need for the same kind of organisation that all multicellular organisms have: </li></ul>Vascular Plant Form & Function cells tissue Tissue systems organs Organ systems 1.Dermal Tissue 2.Ground Tissue 3.Vascular Tissue
<ul><li>Some epidermal cells also produce a waxy layer known as the cuticle. The cuticle prevents water loss and invasion by insects. </li></ul><ul><li>This comprises the outer layer. The kinds of cells found in the dermal layer include: </li></ul>Dermal Tissue 1. Epidermal cells 2. Root Hair cells 3. Guard Cells (Leaves)
The Cuticle - a waxy coating designed to minimize water loss and act as a physical barrier against disease. Upper and Lower Epidermis – an outer layer which does not contain chloroplasts. Their thick walls are helpful for their protective function. Guard Cells – There are spaces in the epidermis called stoma which permit oxygen and water vapour to leave the leaf and carbon dioxide to enter. Each stoma has two guard cells around it, which regulate the opening and closing of the stomates. The structure of leaves is geared to ensure that photosynthesis takes place as efficiently as possible. Leaves are composed of a number of specialised cell types: Leaves
Spongy Mesophyll – active area of photosynthesis. Air spaces are between the cells and are involved in gas excange during photosynthesis. Vascular Bundles – composed mainly of xylem and Phloem. Water, minerals and other dissolved substances are conducted in the xylem, carbohydrates are conducted in the phloem. Palisade Mesophyll – these cells contain the greatest concentration of chloroplasts and is the most active area of photosynthesis.
<ul><li>They absorb water and minerals </li></ul><ul><li>They support plants </li></ul><ul><li>They anchor plants into the soil </li></ul><ul><li>They store carbohydrates e.g. potato </li></ul><ul><li>As roots develop from a seed, the first main root which develops is called the primary root. Smaller roots called secondary roots then develop. </li></ul><ul><li>There are two main kinds of roots: </li></ul>Roots have a number of vital jobs which are important to plants: Roots 1.Tap Roots 2. Fibrous Roots
Monocotyledons – these are fibrous roots that contain many roots of equal size. Monocotyledons also have bands of xylem and phloem around a central region. Fibrous Root System – Draw Picture Cross Section – Draw Picture Dicots – Tap Picture – Draw Picture Vascular Bundle Cross Section <ul><li>Another way of classifying roots is whether they are from a monocotyledon or a dicotyledon. </li></ul>
Root Adaptations – Depth and extent of root systems depends upon: <ul><li>Size of Plant </li></ul><ul><li>Moisture Content of Soil </li></ul><ul><li>How well the plant needs to be anchored in addition, some plants have evolved special structures to cope with extra – ordinary circumstances: </li></ul><ul><li>a) Pneumatophores – grow out of the water to supply the plant with oxygen </li></ul>Dicotyledons – These have taproot systems with vascular bundles containing xylem and phloem vessels. b) Aerial Roots – grow out from leaves to absorb oxygen c) Toxin Releasing Roots – Release substances to reduce competition
<ul><li>The stem section between nodes is called internodes </li></ul><ul><li>Stems have areas of rapidly dividing tissue called meristem. Meristems produce: </li></ul><ul><li>Stems are usually cylindrical to give structural strength. Leaves are attached at points called nodes </li></ul>Stems Primary Tissue – found in short lived herbaceous plants. This tissue is able to photosynthesise. Secondary Tissue – produces woody tissue. This tissue continues to live year after year and evolves into several tissue types. Each year produces a ring of growth.
<ul><li>This accumulation of minerals produces fluid in the xylem that is Hypertonic to the soil outside the root. </li></ul><ul><li>Therefore, water and minerals accumulate in the roots, creating root pressure, leading to the water and minerals being pushed up the xylem. </li></ul><ul><li>Root hairs absorb essential minerals from the soil by active transport. This energy is supplied from internal respiration in the root cells. </li></ul>Water & Food Transport Water Transport <ul><li>As a result; the water enters the root by Osmosis </li></ul>
<ul><li>Water transport up to the tops of trees may be explained using the Cohesion Tension Theory </li></ul><ul><li>This theory is based on a number of properties related to water. </li></ul><ul><li>At best, root pressure is only able to push water up a few metres. Clearly this does not account for the ability of water to travel to the top of trees </li></ul>Adhesion – this is the force of attraction between unlike molecules. Water tends to become attracted to the walls of thin xylem vessels by adhesion.
<ul><li>Water is a polar molecule , with positive and negative ends. This results in water molecules being strongly attracted to each other so that water stays in unbroken columns in the xylem vessels. </li></ul><ul><li>The result is that, as water molecules evaporate and leave the plant through the Stoma (this is called Transpiration ); a negative pressure results which pulls other water molecules up the xylem vessel to replace what is lost. This is called Transpiration Pull and can pull water 100’s of meters against gravity. </li></ul><ul><li>Cohesion . – this is the force of attraction between like molecules. </li></ul><ul><li>Sap can travel at 75 cm per minute. This rate is determined by temperature & wind speed. </li></ul>
<ul><li>The Pressure Flow Theory </li></ul><ul><li>Leaf cells are called The Source </li></ul><ul><li>Root storage cells are called The Sink </li></ul><ul><li>In the leaves, sugars are pumped into phloem sieve tubes by active transport. </li></ul><ul><li>The exact mechanism for food transport is unknown. Phloem cells are living cells, unlike xylem cells, which are dead and hollow. This means that in some way, sugars must travel through the cytoplasm of living cells. </li></ul>Food Transport <ul><li>This causes conditions in the tubes to become hypertonic; causing water to enter from nearby xylem cells </li></ul>
<ul><li>Once in the root, the sugars move into storage cells in the root, closely followed by water molecules moving due to Osmosis. This results in an increase of pressure in the roots, and a decrease in the phloem. </li></ul><ul><li>Therefore, high pressure in the leaves pushes the contents of the phloem tubes; and low pressure in the root pulls on the phloem contents. </li></ul><ul><li>This creates pressure, pushing sugar away from the leaves and towards the roots. </li></ul>
In Monocotyledons – seeds develop consisting of: In Dicotyledons – the contents are much the same except that the seed contains two seed leaves (two cotyledons. <ul><li>Following pollination and fertilization, seeds begin to develop. </li></ul>Seed Growth & Development <ul><li>Embryo </li></ul><ul><li>Food Supply </li></ul><ul><li>A single leaf </li></ul><ul><li>Seed Coat </li></ul>
<ul><li>Factors which determine the onset of germination include: </li></ul><ul><li>Temperature – the exposure to a period of low temperature followed by higher temperature. </li></ul><ul><li>Moisture – Water plays a role in breaking down food reserves which can be used in germination. </li></ul><ul><li>Oxygen – in the soil for cellular respiration </li></ul><ul><li>Once the seed has developed, it often enters a period of dormancy where it remains until certain conditions trigger germination. </li></ul>
Light – This is trapped by Chlorophyll and other Accessory pigments ; although only about 1% of the available light is used. <ul><li>In fact, only certain wavelengths can be absorbed (red and blue are absorbed the best). </li></ul>Day Length – This affects the quantity of light available. The photoperiod increases during the spring, is long during the summer; and decreases to a minimum during fall and winter. Day length plays a role in determining when a plant reproduces. E.g. Chrysanthemums – short days. <ul><li>For plants to grow they need: Light, Carbon Dioxide, Water & Minerals </li></ul>External Factors Affecting Plant Growth
<ul><li>Different plants require different amounts of minerals; and deficiency problems in plants can be diagnosed by soil testing & by careful examination of the plant. </li></ul><ul><li>Some nutrients are acquired due to weathering of rocks including: </li></ul><ul><li>Positive Ions are bound to clay particles. Negative ions are not bound and wash away. This is called leaching. </li></ul><ul><li>17 minerals are required for healthy plant growth. Some are required in large amounts and are called Macronutrients . Others are needed in very small amounts – these are called Micronutrients . </li></ul>Soil Nutrients Potassium Ions (K + ) Calcium Ions (Ca 2+ ) Nitrate Ions (NO 3- ) Sulphate Ions (SO 4 2- )
Light, Gravity, Reproduction, Nutrients <ul><li>Hormones are complex chemicals produced in small amounts; but having large effects. Often they are produced in one part of the plant but affect another. </li></ul><ul><li>There are three groups of plant hormones: auxins, gibberelins, cytokinins. Two others are abscisic acid & ethylene. </li></ul><ul><li>All organisms need to control their growth. Plants use hormones as their form of control. Hormones are used to control many factors such as: </li></ul>Hormones & the Control of Plant Growth
<ul><li>Auxins also regulate: </li></ul><ul><li>Have the effect of causing cells to elongate. This is useful in causing the effect known as photoropism (growth response to light). </li></ul>Auxins Apical Bud Growth Ripening of Fruit and Fruit Drop Cell Division
Gibberelins – Also promote cell division and elongation, particularly just before flowering occurs so that the flower is exposed to insects and wind. Cytokinins – Stimulates cell division, particularly in seeds and fruit. This has proved useful in tissue culture experiments. Ethylene – Important in fruit ripening. Growers store fruit in conditions which prevent its build up to slow down ripening. Ethylene can be added to induce ripening. <ul><li>Synthetic auxins have been developed which are used as weed killers. By stimulating cell division, the plants exhaust their food reserves by growing too fast and die. </li></ul>Abscisic Acid – Inhibits growth. This important effect stops germination during the winter.
<ul><li>Changes in vegetation leads to changes in the Soil, Local Climate, Sunlighy </li></ul><ul><li>Succession occurs in all types of environments; and although these changes vary greatly; eventually, (after 1000’s of years in some cases) a climax community is reached. </li></ul><ul><li>This term refers to changes in the types of vegetation found in a given area and the related changes in animal species found there. </li></ul>Succession
Primary Succession – This process begins when all that is present is bare rock. I.e. no living things exist, no organic material is present. <ul><li>Such an environment is very harsh, which require organisms capable of withstanding extremes of: heat, cold, drought. </li></ul><ul><li>An organism that can do this is known as a Pioneer Organism e.g. Lichens </li></ul><ul><li>A climax community is a self perpetuating environment where succession stops. This is subject to no sudden changes in abiotic factors such as water, temperature and mineral content of soil etc. </li></ul>
<ul><li>As mosses grow faster; Lichens are crowded out and disappear. Thus the vegetation changes the environment, leading to better adapted vegetation taking over. </li></ul><ul><li>This process of change goes through a number of stages. </li></ul><ul><li>In each cases, soil, vegetation and changes in animal populations result in environmental change, which allows new species to arrive, and some of the old ones disappear. </li></ul><ul><li>Lichens bring about changes which begin soil building; making conditions suitable for mosses to grow. </li></ul>
<ul><li>This results in a new community having to be rebuilt from scratch. </li></ul><ul><li>Primary succession is slow, but secondary succession is fast because soil and seeds are present. </li></ul><ul><li>What seeds germinate will depend on environmental conditions </li></ul><ul><li>Sometimes an existing ecosystem can under go rapid change, where almost total destruction can occur e.g. Forest Fire, Flood, Bulldozer </li></ul>Secondary Succession
<ul><li>This may be intraspecific – between organisms of the same species. </li></ul><ul><li>Or, it may be interspecific – between organisms of different species </li></ul><ul><li>Plants may gain a competitive advantage in many ways including: fast growth, producing more seeds, earlier seeds. </li></ul><ul><li>Competition – Often two organisms need the same resource. </li></ul>Competition <ul><li>Competition will affect the direction that succession takes. </li></ul>