Plant project

Christmas Cactus

Scientific name: Schlumbergera bridgesii; monocot

Kingdom: Plantae;

Phylum: Magnoliophyta;

Class: Magnoliopsida;

Order: Caryophyllales;

Family: Cactaceae

Species: Opuntia leptocaulis


The Christmas Cactus is a plant that is mostly found in the South American jungles. The Christmas Cactus can live both indoors and outdoors, but between May and September, it needs less amount of sunlight; too much sunlight can burn the leaves of the plant. Even though the plant is called cactus it is not one entirely, it can store a lot of water and can go without watering for more than a month. They can live in temperatures anywhere from 50 to 65 degrees Fahrenheit. It can be found in colors, white, red, violet, and pink.
9.1
1. Outline the differences between the structure of dicotyledounous and monocotylednous plants

Monocots; Dicots
one cotyledon; two cotyledon
leaf veins are parallel; leaf veins have a net shape
flower in multiples of 3; flower in multiples of 4 and 5
No Secondary growth; Secondary growth
roots are adventitious; roots are develop through radicle



2.Outline the distrubution of tissue and leaf function

Phloem transports the products of photosynthesis (sugars, amino acids).
Xylem transports water and minerals into the leaf tissue from the stem and roots.
Epidermis produces a waxy cuticle for the conservation of water.
Palisade layer which is the main photosynthetic region.
Spongy layer creates the spaces and surfaces for the movement of water and gases.
Lower epidermis contains the stomatal pores which allow gas exchange with the leaf.
The xylem and phloem tissues combine in the vascular tissue to provide support to the leaf.

3.Identitfy Modifications of roots, stems and leaves for different functions

Bulbs: Onions & Lilies
Short vertical underground stems.
Many fleshy highly modified leaves for the storage of nutrient.
Can produce new plants by bulb division or the development of one of the many axillary buds.
These should not be confused with the disc-like Corms found in daffodils and tulips
Stem modification: e.g. Cacti
Leaves are reduced to spines to prevent water loss in transpiration.
The stem is enlarged for the storage of water.
The stem carries out photosynthesis
Carrot: Tap Root modification
Function: Storage of water.
Carrot plants are often associated with very sandy soils. The enlarged root is familiar to those who have eaten the vegetable.
The root modification allows the storage of water in the cortex and central stele.
The mass of the root stabilizes the plant in the loose sandy soils


4. State that dicotyledonous plants have apical and lateral meristems



Plants grow is restricted to 'embryonic' regions called meristems. Having specific regions for growth and development (restricted to just the meristematic tissue), contrasts with animals in which growth takes place throughout the whole organism.
Apical meristems are found at the tip of the root and the shoot, adding growth to the plant in these regions. The apical meristems are described as indeterminate , this type of growth tends to add length to root and stem in 'module' or 'units' (described below). This tissue remains 'embryonic' for prolonged periods of time and in some cases over 100's of years. Contrast this with the more determinate growth of leaves, petals and flowers in which a very precise growth occurs.

5. Compare growth du to apical and lateral meristerns in dicot/ledonous plants

Apical meristem of the apical bud adds new tissue to the stem tip. This addition increases the length of the stem.
Stem growth The tissue added includes the units described below:
1. Adds length to the stem and root
2. Added in modules.
3. Each module is added at the meristem and includes leaf (leaves), internode length of stem and axillary buds.Stem differentiation at the apical meristem.
These diagrams illustrate that the tissue added at the apical meristem differentiates into the various primary plant body structure This tissue diagram is a cross section of the stem of the primary plant body.
This means that there has been no additional secondary thickening of the cell walls.

6. Expalin the role of auxin in phototropism as an of the countrol of plant growth

A tropism is a bending-growth movement either toward or away from a directional stimulus.
Phototropism is the bending-growth towards the unilateral source of light.
Auxins are a class of plant growth hormones (growth regulating factor)
Auxins are one of atleast three major classes of plant growth regulators. Unlike animal hormones plant hormones can provide a range of responses from the tissues.

9.2 Tranpsport in Angiosperms

1. Outline how the root system provides a large surface area for mineral and warer uptake
The monocotyledon root has a fibrous highly branching structure which increases the surface area for the absorption of water.
Dicotyledon root structure has a main tap root and often a surface branching root system for the absorption of surface run off.
Deeper in the soil the tap root branches to access deeper water and mineral.Behind the apical meristem of the root there is a zone of differentiation of the epidermis called the root hair zone.
Root hairs increase the surface area available to the root cell to absorb water.The extension of the cell wall increases the surface area for the absorption of water and minerals at the cellular level.
The root hair cell provides both an increase in the cell wall (apoplastic pathway) and the cytoplasmic route (symplastic pathway) for the movement of water.

2. List ways of movement of minerals to the root.

Minerals move to the root system by the following pathways:
Diffusion which requires a concentration gradient (Note that in general minerals are in very low concentration in soil).
Fungal hyphae in mutualistic relationship with the plant root provides minerals such as nitrates. Fungal hyphae form a network (mycelium) that increases the surface area within the root to concentrate minerals.
Mass flow of soil water (minerals solutions).
Mass flow is a hypothesis to explain the movement of solute by means of a hydrostatic pressure gradient, not osmotic gradient.
Water is being taken up at the root which produces a negative pressure potential.
Minerals dissolved in water form hydrogen bonds with water such that the movement of water towards the root 'drags' the minerals with the water.
The mass flow of the solutions of mineral ions towards the root 'concentrates' them for absorption

3. Explain the processs of mineral ion absorption from the soil into roots by active transport

Any fertile soil contains at least some clay particles within its structure.
Clay particles carry a negative electrical charge to which the mineral ions (K+, Na+, Ca2+) attach.
This attachment effectively prevents the leaching of the mineral ions from the soil. Unlike animal cell there are no potassium-sodium pumps in the cell membranes of plant cells. Rather there are proton pumps which pump protons ( H+) outside of the cell. This creates an electro-negative charge within the cell.2. When the root cells secrete protons into the surrounding soil water the hydrogen ions displace the mineral ions from the clay particle, freeing them into solution.
3. The mineral ions in the soil water are free to be absorbed by various pathways.


Absorption of mineral ions.
The plasma membrane of the plant cell can bring about the absorption of mineral by two different energy demanding processes:
Indirect method in which proton pumps (hydrogen pumps) establish electrochemical gradients
Direct method in which membranes actively transport a particular mineral.
Indirect processes:
Proton (hydrogen) pumps in the plasma membrane pump out hydrogen ions (H+) this has a number of effects.
. Hydrogen pumps of the plasma membrane actively pump hydrogen ions out into the soil water. This creates a membrane potential of -120 mV.
2. Hydrogen ions combine with anions such as Cl- in W or membrane carriers allow the uptake of the ion against the electrochemical gradient(3.).
4 H+ displace cations (e.g. K+) from the clay particles so that they are free to move down an electrochemical gradient by facilitated diffusion (5).
Note that both these pathways still rely on the initial active (needs energy) step of proton pumping.

4.State that terrestrial plants support themselves by means of thickened cellulose and lignified xylem

thickened cellulose: both xylem and pholem cells have thick secondary cell wall composed primarily of cellulose, providing rigidity.
Cell tugor; plant celll vacuoles have low water potential; water enters the cell and vacuole by osmosis causing the cell to swell against its wall with a pressure against the cell wall which procvides rigidity
lignified xylem: vascular tissue cells reinforce with helical or ring-shaped thickening of the cellulose cell wass impreganted with ligin, which makes the cell walls hard, providing resitance to pressure

5.Definition of Transpiration

Transpiration is the loss of water form the leaves and stem of plants.

6.Expalin how water is carried by the transpiration stream

The leaf adsorbs light on it large surface area.
Heat is produced.
Water in the spongy mesophyll tissue enters the vapour phase.
There is a humidity gradient between the spongy mesophyll which is saturated with water vapour and the surrounding air.
Water evaporates through the stomatal pore down a humidity gradient.
The evaporation of water draws (pulls) more water by mass flow into the spongy mesophyll space.
Water molecules are held together cohesion due to hydrogen bonds between water molecules.
In turn this draws water from the end of the xylem by the same cohesion.
Water is therefore drawn up the stem by cohesion between water molecules and adhesion to the xylem vessel walls.
This transpiration 'pull or tension' extends all the way down the xylem to the root.
Uptake of water beginning in the roots:

Water enter the root by osmosis because the soil water has a lower solute concentration of minerals than the epidermal cell cytoplasm (there is a water potential gradient).
Water movement across the cortex cell is by two pathways both involving a water potential gradient. The cortex cell cytoplasm has a solute concentration gradient. This moves water symplastically from cell to cell by osmosis. The Apoplastic pathway moves water by capillary action of mass flow through the connecting cellulose cell wall.
The endodermis marks the beginning of the central stele of vascular tissue. Both minerals and water must pass through the plasma membrane of the endodermis.
Water enters epidermal cell cytoplasm by osmosis. The solute concentration is lower than that of soil water due to the active transport of minerals from the soil water to the cytoplasm.
Symplastic Pathway (b) to (d): water moves along a solute concentration gradient. There are small cytoplasmic connections between plant cells called plasmodesmata. In effect making one large continuous cytoplasm.
Apoplastic Pathway(e) to (f):water moves by capillarity through the cellulose cell walls. Hydrogen bonding maintains a cohesion between water molecules which also adhere to the cellulose fibres.
(g) The endodermis is the outer tissue of the vascular root tissue.

The casparian strip of the endodermis is a barrier to the movement of water of minerals by the apoplastic pathway. All solute and water must move through the plasma membrane of the endodermal cells before entering the stele
The cellulose cell wall contains a strip (casparian strip) of a waxy water repellant substance called suberin.
The suberin prevents water and dissolved minerals from passing into the xylem by the apoplastic pathway.
Therefore water solution must pass through the plasma membrane of the endodermis. The endodermis plasma membrane can then selectively control mineral uptake and rate of uptake.
Minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel. Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration of large plants.
Minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel.
Chloride for example is actively pumped of pericycle (or endodermal) cells.
This creates a water potential gradient that moves water passively into the xylem.
Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration
Rather the pressure potential gradient (hydrostatic pressure) based on evaporation (tension) form the leaf is responsible for the upward movement of water in the xylem.
However, consider that many plants live in very humid environments where evaporation rates may not be that great. For small plants, the process of gutation has been observed in which water weeps from the stomatal pores in liquid rather than vapour phase.
Xylem vessels form a continuous pipe from the root up through the stem. along petioles to the leaf.
Xylem cells are produced from the division of the cambium and then differentiation into xylem
The cytoplasm full breaks down and the end wall break down to form the pipeline
To support the cell wall extra thickening take place. This often has characteristic patterns. Some spiral some annular This extra thickening resists the 'tension' created by the rate of evaporation


Water molecules are weakly attracted to each other by hydrogen bonds (Cohesion). This action extends down the xylem creating a 'suction' effect.
There is also adhesion between water molecules and the xylem vessels
The cohesion and adhesion act together to maintain the water column all the way up from the root to the stomata.
The rapid loss of water from the leaf pulls the water column stressing the cohesion and adhesion between water molecules. This creates 'tension' within the xylem vessel sufficient to cause the walls of the xylem to be bent inwards.
In large trees this tension can be so great that the diameter of the tree can decrease during the summer months with peak rate of transpiration
Some of the light energy absorbed by the large surface area of the leaf is changed to heat.
The heat raises the temperature of the leaf and water in the spongy mesophyll tissue is changed into water vapour.
There is 100% saturation of the sub stomatal air space (b) which contrast with the very low % saturation of air with water vapour.
With the stomatal pore open this gradient operates only over one cell thickness.
Water evaporates into the air
The water loss from the leaf draws new water vapour from the spongy mesophyll (symplastic & apoplastic movement) into the sub stomatal air space.
In turn the water molecules of the mesophyll space draw water molecules from the end of the xylem

7.Guard cells and transpiration regulation.

Stomata ( singular Stoma ) are pores in the lower epidermis.
Each stomata is formed by two specialised Guard Cells.
The epidermis and its waxy cuticle is impermeable to carbon dioxide and water.
During the day the pore opens to allow carbon dioxide to enter for photosynthesis. However the plant will experience water loss. If the water loss is too severe the stoma will close.
During the night plants cannot photosynthesis and so the plant closes the pores thereby conserving water.
The movement of water is an example of mass flow due to a negative pressure potential.


8.State the plant abscisic hormone acid causes the closing of the stoma.

Plants have a mechanism which closes the stoma at night. However when a plant is suffering water stress (lack of water) there is another mechanism to close the stoma.
(a) dehydrated (low water potential) of the mesophyll cell causes them to release abscisic acid.
(b) Abscisic acid stimulates the stoma to close.

9. Explain how abiotic factors affect the rate of transpiration in typical terrestrial plants.

The greater the rate of transpiration the greater the waterloss from a plant. Most of this waterloss occurs through the stoma with other surfaces adapted to reduce such losses.
Brown & Escombe(1900) showed that although the stomatal pore is small the sum of the circumferences of the pores in a leaf effectively mean that with the pores open, there is no lower epidermis!
The rate of evaporation is proportional to the diameter of the pore not the surface area of the pore. In the diagram the sum of the transpiration of water vapour through the small pores (B) is greater than the larger pore.
At the edges the molecules of water vapour are able to fan out in many directions and avoid the gradient of water vapour concentration in the vertical plane.
Humidity
This is a measure of the water vapour in air and is normally expressed as a percentage.


Light absorbed by the leaf warms the water within the mesophyll tissue and it enters the vapour phase in the space above the pore called the sub stomatal air space (SSAS).
With the pore open water vapour diffuses out down a step water vapour gradient.
The water vapour forms diffusion shells of changing % humidity.
The steepest gradient is found at the edge of the pore where effectively most waterloss occurs.
The significance of Brown & Escombe's research now becomes evident


In high humidity the diffusion gradient is not as steep and the rate of diffusion is less.
In high humidity the diffusion shells of water vapour from one pore to the next joint and the steep gradient associated with the edge of the pore is lost.
The formation of this boundary layer of high humidity reduces the rate of transpiration.

2. Wind:
Moving air reduces the external water vapour concentration such that the gradient between the sub stomatal air space and the surrounding air increases.
Still air allows the build up of boundary layers as shown above and so reduces the rate of transpiration.
3. Temperature:
The leaf absorbs light and some of the light energy is lost as heat. Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as it does at 20°C. The effective evaporation is in the sub stomatal air space and increases the gradient of water vapour between the sub stomatal air space and the surrounding air.

4. Light:
The rate of plants transpire is faster in the light than in the dark. This is because light stimulates the opening of the stomata and warming of the leaf. The mechanism of pore opening relates to the Guard cell becoming turgid. The mechanism:

(a) The guard cell absorbs light and produces ATP in the light dependent reaction.
(b) The ATP is used to drive proton pumps that pump out H+ . The inside of the cell becomes more negative.
(c) Potassium ions enter the cell which increases the solute concentration.
(d) Water moves from the surrounding tissue by osmosis.

The turgid cell increases the pressure potential and the cell expands.
The cells have asymmetric thickening with lignin on the stoma-side wall.
The cells expand more on the outside wall.
The pore opens in the middle as each cell bends.

10. Outline four structural adapttations of xerophytes

reduces leavw: minimizes water loss by reducing leaf surface area
thickened waxy cuticle: minimizes waster loss by limiting water loss thorough epidermis
reduced number of stomata: minimizes water loss through leaves
succulence: stems specialized for water sotrage maximzes retention of water available during infrequent rains

11. Outline the role of pholem in active translocation

Translocation moves the organic molecules (sugars, amino acids) from their source through the tube system of the phloem to the sink. Phloem vessels still have cross walls called sieve plates that contain pores.
2. Companion cells actively load sucrose (soluble, not metabolically active) into the phloem.
3. Water follows the high solute in the phloem by osmosis. A positive pressure potential develops moving the mass of phloem sap forward.
4. The sap must cross the sieve plate. Current hypothesis do not account for this feature.
5. The phloem still contains a small amount of cytoplasm along the walls but the organelle content is greatly reduced.
6. Companion cells actively unload (ATP used) the organic molecules
7. Organic molecules are stored (sucrose as starch, insoluble) at the sink. Water is released and recycled in xylem

Plants will not transport glucose as it is used directly in respiration and is metabolically active. Sucrose is soluble and transportable but not metabolically active in respiration. At the sink it is necessary to have the transported molecule insoluble (no osmotic effect) and inactive ( no respiration effect).
Sources could be a photosynthesising leaf or a storage region at the beginning of a growing season (Tuber)
Sinks could be the growth point on a stem or the storage area at the end of a growing season (tuber)
The hypothesis does not account for how the direction of sap travel could be reversed nor does it explain how the resistance of the sieve plate could be overcome.

9.3 Reproduction in Flowering Plants

1. Distinguish betweem

Pollination: transfer of pollen grains from the anther to the stigma
Fertilization: fusion of male and female gametes
seed dispersal: mechanisms for distributing seeds away from the parent plant

2. Explain the conditions need for the germination of a typical seed.


oxygen for aerobic respiration
water to metabolically activate the cells
temperature for optimal function of enzymes
for their successful germination. Each seed has its own particular combination of the above three factors.
It maybe that in a particular species these processes need to be proceeded by other more specialised conditions such as:
fire
freezing
passing through digestive system of a seed dispersing animal
washing to remove inhibitors (beans)
erosion of the seed coat (Poppy)

3. Outline the metabolic processes during germination of a starchy seed

The metabolic events of seed germination:
a) Water absorbed and the activation of cotyledon cells
b) Synthesis of gibberellin which is a plant growth substance. (Hormone is some text longer a term used to describe such compounds).
c) The gibberellin brings about the synthesis of the carbohydrase enzyme amylase
d) Starch is hydrolysed to maltose before being absorbed by the embryonic plant
e) The maltose can be further hydrolysed to glucose for respiration on polymerised to cellulose for cell wall formation

6. Explain how flowering is controlled in long day and short day plants, including the role of phytochrome

Phytochrome is a pigment that exist in plants in two forms
Pr, absorbs white/red light
Pfr, absorbs dark/far- red light in white or red light Pr id converted to Pfr
in far red light or in darkness, Pfr gradually reverts to Pr
Pfr acts as a promoter of flowering in long-day plants
Pfr as an inhibitor of flowering in short- day plants

sources: clik4biology.info and Plant packet