Biology of Plants

Plant Gas Exchange

Occurs by direct diffusion with the surroundings in the leaves, stems and roots for plants lack organs for this process.

1.      Roots: Between cells at the exterior of the root hairs and air spaces in the soil

2.      Stems: Openings between cells called lenticels that permit movement of air around them = surface for the exchange of gases

3.      Leaves: Through small pores called stomata which are found on many plant surfaces but mainly on the underside of leaves. (Away from the drying effects of the sun) The size of the stoma (pore) is controlled by 2 crescent shaped guard cells which have a thin and elastic outer wall and thick and rigid inner wall. The opening and closing of the stomata is influenced by the amount of light, H₂O and CO₂

i) An increase in the degree of light = opening of the stomata so CO₂ can be utilized for photosynthesis

ii) A low level of CO₂ will cause the stomata to open

iii) If water is abundant the stomata will open to result in an increased transpiration flow

iv) If water is scarce the stomata will close to reduce water loss = prevents loss of turgor pressure and wilting

Opening/closing of stomata:

a) Water moves into the guard cell that causes the outer surface to bulge and the inner surface to buckle – the elasticity of the outside wall and the rigidity of the inner wall causes the inner wall to buckle inwards = opens the pore

b) An osmotic gradient between the guard cells and its surrounds causes water to move into them

c) This osmotic gradient is caused by an increase in sugars in the guard cell by it performing either photosynthesis or by enzyme action.

d) The opening and closing of the stomata is one of the ways plants control the rate of transpiration

Leaf

Tissue is adapted to receive light for photosynthesis, permit the movement and uptake of water and allow for gas exchange. The external structure of a leaf:

1.      Petiole: Narrow stalk that attaches the leaf blade to the stem

2.      Lamina (blade) is the photosynthetic portion of the leaf that is generally flat and thin to decrease surface area for the absorption of light

3.      Midrib and veins enter the blade via the petiole and consist of vascular tissue which is subdivided into small vessels so that all the cells are in close contact with the plant circulatory system.

4.      Surfaces: Abaxial = upper Adaxial = lower Isobilateral = same surface

3 main internal tissue regions in a leaf:

1.      Epidermis which consists of:

a) Cuticle: Waxy layer covering the leaf surface that prevents excessive water and gas loss. Varies in thickness depending on leaf and habitat type

b) Epidermal cells: Protect upper and lower leaf surfaces, containing stomata which regulate transpiration and gas exchange

2.      Mesophyll which consists of:

a) Palisade mesophyll: Cells that contain chlorophyll – the active sites of photosynthesis and lie directly under the upper epidermal cells
b) Spongy mesophyll: Irregularly shaped and loosely arranged cells that have few chloroplasts and are surrounded by air spaces for stomata in the lower epidermis.

3. The vascular tissues: xylem (strong thick pipes) and phloem (thinner tubes) that make up the plant transport system

Root Structure:

1.      Epidermis: Single cell layer with long extensions = root hairs which increase surface area

2.      Cortex: Thick layer of packing cells often containing stored starch

3.      Endodermis: Single layer of tightly packed cells containing a waterproof layer = casparian strip that prevents the movement of water between cells

4.      Pericycle: Layer of undifferentiated meristematic (growing) cells

5.      Vascular tissue: Contains xylem and phloem cells which are continuos with the stem vascular bundles. The arrangement is different and the xylem usually forms a stat shape with 2-6 arms

Root Tip Structure:

1.      Zone of elongation: Area behind the meristem where new cells increase in length

2.      Meristematic zone: Behind the root cap – zone of cell division

3.      Root cap: Protective layer of cells covering the delicate area of dividing cells that aids in soil penetration

Root Hair:

Single celled extensions of the epidermal cells that are located on the maturing area of the root close behind the root tip. They provide increased surface area and thus more efficient absorption of water and minerals from the soil.

Stem Structure:

1.      Epidermis: One cell thick that secretes a waterproof cuticle in younger plants and may be replaced in older plants by bark

2.      Cortex: Composed of various “packaging cells” that are the source of plant fibres such as sisal and hemp and give young plants strength and flexibility

3.      Vascular tissue: Contains phloem and xylem tissue which grow out from the cambium. In dicot (broad leaved) plants the vascular tissue is arranged in vascular bundles with phloem on the outside and xylem on the inside. In older plants the xylem bundles fuse together to form the bulk of the stem

4.      Pith: Central region of a stem used for food storage in young plants but may be absent in older plants (they’re hollow)

Xylem Tissue

Composed of dead cells joined together to form stiff long empty tubes that are impermeable and strengthened with fibres. Different kinds of cells form wide and narrow tubes and the end cells walls are either full of holes or are absent completely. Before death the cells form thick cell walls containing lignin which is often laid down in rings or helices and make the xylem vessels very strong so they don’t collapse under pressure also making the woody stems strong.

Phloem Tissue:

Composed of sieve tube cells which form long columns with holes in their end walls called sieve plates. These cells are alive with walls made of cellulose and are permeable but lose their nuclei and other organelles, and their cytoplasm is reduced to strands around the edge of the cells. These strands pass through the holes in the sieve plates = continuos filaments (perforated end walls) and the centre of these tubes is empty. Each sieve tube cell is associated with one or more companion cells with nuclei and organelles and are connected by plasmodesmata, (cytoplasm) that provide them with proteins, ATP and other nutrients.

Description	Xylem	Phloem
Cell Wall Thickness	Thick	Thin
Cell Wall Material	Linin	Cellulose
Permeability	Impermeable	Permeable
End Walls	Absent	Seive plates
Function	Transport H2O/minerals	Transport food
Carried to	Leaves	All parts of plant
Direction of Flow	Upward	Up and down
Also Has	Fibres for stength	Companion cell for control

Water Flow in Plants:

1.      Continuos stream entering via the roots where it flows upwards in the xylem to evaporate from the surface of the leaf via the stomata

2.      Evaporation of water from the lead surface is the force by which water is drawn upwards via the roots to the leaves. Transpiration = Drawing of water upwards through the plant by evaporation

3.      Transpiration is important because:

a) Evaporation causes cooling = prevents damage by sunlight

b) Water is transported to the sights of photosynthesis

c) Cells in the leaf are kept moist which is necessary for gas exchange (gases must be in solution)

4.      Force of transpiration is strong enough to lift water up tall trees

5.      An osmotic gradient generates the movement of water from the xylem in the leaf to the stomata. Water concentration is higher in the porous xylem than in the surrounding cells = water flows in this direction and the osmotic gradient is maintained by evaporation.

6.      A pressure difference assists movement of water through the xylem because a low water pressure created by evaporation causes water to be drawn up through the xylem in the root.

7.      Root hair actively transports inorganic nutrients and salts which has the effect of increasing the concentration inside root cells. Therefore water flows osmotically as there is a lower concentration of water in the root cells. The build up of water in the roots is called root pressure and forces water up the xylem vessels which can result in small droplets of water being squeezed out at the top of the leaf. This is called guttation

8.      Root pressure can push water up about 10cm = isn’t as effective as transportation

9.      3 other physical factors of water assist in the process of respiration:

a) Capillarity: Forces of attraction between walls of the tube and the liquid in it = the smaller the diameter the greater the force of attraction

b) Adhesion: Force of attraction between unlike molecules that assists the capillarity and supports the water column all the way up to the leaves = There’s a force of attraction between the xylem walls and the water

c) Cohesion: Force of attraction between like molecules which aids the passage of water by maintaining the upward pull. As water is evaporating the osmotic movement of water molecules attracts others to them.

Transpiration Rate Factors:

1.      Humidity: Increase in the levels of atmospheric water between the plant and the air surrounding it will reduce the transpiration rate

2.      Wind: Air movement naturally increases evaporation = increased rate of transpiration

3.      Temperature: Increase will increase the amount of evaporation = increase in the rate of transpiration

4.      Soil moisture: A plant requires water in the soil to replenish the water it loses through evaporation = effects the rate of transpiration

Translocation:

Involves the active dumping of materials which requires energy as is why phloem cells must be living.

1.      Movement of materials within the plant = specifically the movement of the products of photosynthesis to areas of the plant in which they are needed. Eg. Supply energy for active transport of inorganic materials and ions by the root hairs

2.      Different to transpiration = movement of substances up and down the through plant tissues

Chloroplasts

The site of photosynthesis – composed of stacks of thylakoid discs (with chlorophyll in each disc) called grana suspended in a fluid matrix called stroma while the organelle is surrounded by a double layered membrane.

Photosynthesis:

6CO₂ + 12H₂O + Solar Energy = C₆H₁₂O₆ + 6O₂ + 6H₂O occurs in the chloroplasts. There are 2 phrases of photosynthesis – the light and dark reactions:

Light Reaction:

Changing of light energy to chemical energy which is stored in ATP and NADPH but only occurs in the presence of light. Occurs in the thylakoid membrane.

1.      Light strikes a de-energised chlorophyll molecule which energises its electrons which move to the other boundaries of the chlorophyll molecule

2.      Chlorophyll is now classified as an energy carrier

3.      Some of the energy from these energised chlorophyll electrons is used to synthesise ATP from ADP + P

4.      The rest of the energy is used to split into H + O : H₂O = 2H + 2e- + O

5.      The oxygen is released into the atmosphere

6.      The 2 protons and 2 electrons are trapped by NADP to carry H = NADPH

7.      The NADPH and ATP are used in the dark reaction

Dark Reaction:

Doesn’t require light as the hydrogen carried in the NADPH is combined with CO₂ to become glucose – the energy to perform this is provided by the light reaction.

1.      Takes place in stoma within the chloroplast

2.      DADPH and ATP move from the thylakoid to the stroma

3.      This process fixes CO₂ to become glucose in the Calvin Cycle.

_4.        The CO₂ is fixed by ribosome diphosphate (RDP) RDP is a 5-carbon sugar which becomes an unstable 6-carbon sugar once it fixes the _CO2

5.      6-carbon sugar breaks down into 2 3-carbon molecules of phosphoglyceric acid (PGA)

6.      At this stage energy from ATP made in the light reaction combine PGA with 2H supplied by NADPH from the light reaction

7.      This forms PGAL which can be used as a nutrient or converted into either:

a)      RDP which can combine with CO₂ (and repeat the process)

b)      Glucose

Pigment

Substances which absorb light energy so it can be used by living organisms. Chlorophyll is the pigment used in photosynthesis that absorbs violet, blue and red light and reflects green light.

Photosynthesis and Respiration Balance:

1.      Plants respire and photosynthesise

2.      Certain cells in plant tissues constantly carry out the process of cellular respiration that is unlike the process of photosynthesis which only occurs at certain wave lengths

3.      Plants that are photosynthesising at a greater rate than they are respiring have a net production of oxygen and a net utilization of CO₂

4.      Plants that are respiring at a greater rate than they are photosynthesising have a net production of CO₂ and a net utilization of oxygen

5.      Plants do not reach a point where there is equal balance between the processes of photosynthesis and respiration. This is the compensation point = situation where the amount of CO₂ produced by cellular respiration is equal to that utilized by the process of photosynthesis.

Photosynthesis	Respiration
Food is accumulated	Food is broken down
Energy from the sun is stored in glucose	Energy from glucose broken down by oxidization
Oxygen is given off	Oxygen absorbed
Produces glucose	Produces CO2 and H2O
Goes on only in the light	Goes on day and night

Biological Classification Test Notes

Characteristics of Living Beings:

Characteristics that all things have in common at some point in their life:

1. Movement: Locomotion of at least part of an organism’s body.

2. Nutrition: Required by organisms to provide energy, enable growth, maintain and reproduce themselves. Can be either heterotrophic or autotrophic.

3. Growth: The development of an organism to increase size, by in-taking food substances different than themselves and changing it chemically to allow their cells to increase in size and number.

4. Respiration: Energy is obtained from food in a chemical reaction which usually requires oxygen and produces carbon dioxide, water and energy. This process is called respiration.

5. Reproduction: Production of new individuals from existing ones.

6. Excretions: Removal of waste products of metabolism from the body.

7. Response: An organism’s ability to respond to changes in both the internal and external environment.

Heterotrophic:

When an organism survives on the intake of organic matter derived from other living organisms. It is therefore dependant on other organisms.

Autotrophic:

The ability of an organism to derive nutrition through either photosynthesis or chemosynthesis. It is therefore able to produce its own food.

Photosynthetic:

An organism’s ability to use the process of photosynthesis to produce its own food.

Chemosynthetic:

The ability to use chemical reactions to produce their own food, like anaerobic bacteria.

Asexual:

Reproduction requiring only one parent – offspring are genetically identical to their parent.

Sexual:

Reproduction requiring both a male and female parent.

Death:

When an organisms life processes stop.

Metabolism:

The ongoing interrelated series of chemical reactions taking place in a living organism that provide the energy and nutrients required to sustain life.

Classification:

The grouping together of organisms which demonstrate similar structures – this is called natural classification. It is based on relatedness and shows genetic as well as revolutionary relationships.

Hierarchical System of Classification:

Classification is based on a system of hierarchy. As we move down each level the similarities become greater and the differences fewer. These levels or the hierarchy are:

1. Kingdom;

2. Phylum;

3. Class;

4. Order;

5. Family;

6. Genus;

7. Species.

Taxon:

The groups to which organisms are assigned to.

Dichotomous Key: A key where different organisms are separated.

Substrate:

Molecules that react.

Organelle:

Membrane-bound subdivision of the cell, specialised for a specific function.

Symbiotic Relationship:

The relationship between two organisms where they cannot be separated from the other and survive.

Epiphytic:

A plant that grows on top of another or is supported by another plant but does not depend on it for nutrition.

Enzymes:

Protein produced by living cells that promotes a specific biochemical reaction by acting as a catalyst.

Catalyst:

A substance that increases the rate of a chemical reaction without itself undergoing any change.

Genes:

The basic unit capable of transmitting characteristics from one generation to the next. It consists of a specific sequence of DNA or RNA that occupies a fixed position (locus) on a chromosome.

Chromosome:

Rod-shaped structure in a cell nucleus carrying the genes that determine sex and the characteristics an organism inherits from its parents.

Gamete:

Reproductive cell which is either male or female with half the normal number of chromosomes that unites with another cell of the opposite sex.

Cotyledons:

The leaf or leaves produced by the seed of a flowering plant.

Prokaryote Cells:

Are small and do not have a membrane bound nucleus. Bacteria, cyanobacteria and blue-green algae are made up of these cells. Prokaryotic organisms perform specialised tasks but without organelles. Instead chemical reactions are used within the various regions of the cell.

Eukaryote Cells:

Contains a membrane bound nucleus. Plants, animals, fungi and protists are made up of these cells. Eukaryotic organisms possess membrane bound organelles which preform specialised tasks – eg. The mitochondria carry out respiration.

Kingdom Monera:

Bacteria:

1. Are unicellular;

2. Made up of prokaryotic cells;

3. Contain RNA and DNA;

4. Divide by binary fission 

5. Most are surrounded by a rigid cell wall;

6. May be motile using flagella;

7. Some form bacill; (Spores which are very difficult to kill)

8. Three main shapes: Spherical (Cocci)

                                  : Coiled (Spirilla)

                                  : Rod shaped (Bacilli)

9. Are classified using: size, shape, colour, reaction to stains and reactions to various conditions.

10. To survive bacteria generally require moist conditions to grow and reproduce. However different species have different temperature optimums and preferences.

11. Aerobic bacteria require oxygen for respiration while others are anaerobic and do not require oxygen to survive.

12. They can be autotrophic, chemosynthetic or heterotrophic.

13. Eventually all naturally occurring substances can be broken down by bacteria.

Kingdom Protista:

1. Contains algae, protozoans, water moulds and slime moulds.

 2. Most are single celled, but some are multicellular like brown kelp which can grow to be 60 metres long.

3. Although some may be plant-like, fungi-like or animal-like they lack the specialised features of these groups.

4. Occur in aquatic or at least moist environments.

5. May be free-living but some are parasite which cause disease.

Algae Classification:

Algae are classified according to their colour:

1. Dinoflagelletes and golden algae are microscopic plankton that are yellow-brown in colour.

2. Rhodophyta: Red algae

3. Phaeophyta: Brown algae

4. Chloraphyta: Green algae

Kingdom Fungi:

1. Secrete enzymes over the surface of their food and absorbs the broken down products directly.

2. Non-motile like plants.

3. Do not photosynthesise.

Made up of tiny threads called mycelium and reproduce by spores. Examples include bread mould, yeast, mushrooms, smuts and rust. 

Lichens:

Are the result of a symbiotic relationship between algae and fungi.

Kingdom Plantae:

Plants are classified on the basis of constituent characteristics: such as structure. They are divided into two main groups:

1. Bryophytes: Which lack conducting tissue (veins) such as mosses and liverwort.

2. Tracheophytes: Are the largest group and contains all the “modern” plants such as grasses and trees.

Phyllum Bryophytes:

1. Are simple plants;

2. Lack tree roots;

3. Lack true stems and leaves;

4. No vascular tubes;

5. Small and clumping;

6. Require moist environments;

7. Have a reproductive cycle which contains both an asexual (spore) and sexual stage.

Phyllum Tracheophytes:

Can be divided into a variety of groups based on their structural characteristics. Most vascular plants have a well developed shoot and root system.

Phylum Pteridophyta (Filicopsida):

1. The group of ferns;

2. Reproduces through spores;

3. Usually ground plants but may be epiphytic; (tree-like)

4. Live in most environments; (free swimming sperm)

5. Have alternation of generation. (a two part lifecycle)

Phylum Coniferopsida:

1. Conifers: Pines, cypresses, cedars and redwoods and are found mainly in the northern hemisphere;

2. Mostly large, woody land plants;

3. Usually scale-like needle leaves;

4. Gametes produced in separate cones;

5. Naked seeds develop in cones. (not enclosed in fruit)  

Phylum Ginkopsida:

1. Ginkgo or maiden-hair tree;

2. Large woody tree;

3. Fan-shaped deciduous (sheds in autumn) leaves with veins branching in twos;

4. Distinct male and female plants;

5. Seeds naked on scales.

Phylum Cycadopsida:

1. Cycads;

2. Palm-like plants;

3. Leaves are large and subdivided in a pinnate way; (resembling a feather)

4. Gametes produced in cones on different plants;

5. Cones are massive and fleshy;

6. Seeds naked on scales of cone.

Phylum Angiospermae:

1. Flowering plants, grasses, herbs, shrubs and trees;

2. All produce flowers;

3. Produce seeds inside a specialised fruit;

4. Divides into two subclasses: Monocotyledonae (one seed leaf) and dicotyledonae (two seed leaf).

Class Monocotyledonae:

1. Stem anatomy: Vascular bundles are scattered

2. Seed morphology: Embryo has one cotyledon (seed leaf).

Class Dicotyledonae:

1. Stem anatomy: Rings of vascular bundles

2. Seed morphology: Embryo has two cotyledons (seed leaves).

Kingdom Animalia:

1. Phyllum Porifera – Sponges

2. Phyllum Coelenterata (cnidaria) - Jelly fish, corals

3. Phyllum Platyhelminthes (flatworms) – Planaria, liver flukes, tape worms

4. Phyllum Nematodes (roundworms) – Ascaris, thread worms.

5. Phyllum Molluscs: Gastropoda – Snails, slugs

                   : Bivaloia – Oysters, clams

                   : Cephlapoda – Squid  

6. Phyllum Annelida – Worms

7. Phyllum Arthropoda – insects, spiders, centipedes, crabs

8. Phyllum Echinodermiata – starfish, sea urchins

9. Phyllum Chordata: Fish, amphibians, reptiles, birds, mammals

Vacuole:

Cellular inclusion which is small in animals (used for food storage and digestion) and big in plants (used for storage and osmotic control).

Centrioles:

Paired tubular structure found in animals and algae which is involved in cell division.

Turgorpressure:

Water in cell allows it to maintain its shape. Plant with low turgorpressure = wilts.

Plant & Animal Cells:

Plant Cells	Animal Cells
Cell Wall: Mixture of carbohydrates including cellulose	No Cell Wall but may have  carbohydrate coat
One large vacuole - up to 90% cell volume	Vacuole absent or small
Chloroplasts in photosynthetic cells	No chloroplasts
Centrioles absent	Centrioles (involved in spindle formation) present

Cell Parts:

1. Nucleus: Controls metabolic (cellular function)

2. Cell Membrane: Support and define cell, gives shape and controls movement into and out of the cell.

3. Cell Wall: Found mainly in plants; (but also in bacteria) support cell by turgorpressure.

4. Cytoplasm: Jelly that supports the organelles.

5. Mitochondria: Power house of the cell where respiration occurs (burning up of glucose and fat to create energy).

6. Endoplasmic reticulum: Tubes that connect nucleus to the outside world so it can adjust to changes.

7. Chloroplasts: Site of photosynthesis using chlorophyll – green pigment.

8. Ribosome: Site of proteinsynthesis.

Isotonic:

Having the same concentration as the surroundings.

Movement of cellular substances:

Is dependant upon 3 biological principles.

Diffusion:

Occurs naturally and is the movement of molecules amongst themselves. This is the result of molecular collision which results in the gradual spreading out of molecules until there is an even distribution. This is called the diffusion gradient.

The rate of diffusion is affected by the objects concentration, the temperature and the pressure.

Osmosis:

Occurs with a selectively permeable membrane where the smaller molecules move by diffusion through the membrane. Since larger molecules cannot defuse a concentration difference is created. The diffusion of water through a selectively permeable membrane. This transports the water from an area of high concentration to an area of low concentration.  

Active Transport:

When the cell membrane extracts molecules against the concentration gradient = energy is expended.