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General Characters of Bryophytes

DIVISION BRYOPHYTA:




Definition:

Bryophytes can be defined more precisely as plants with the distinguishing characters as follows:
  • Vascular system absent
  • Gametophyte dominant
  • Sporophyte attached to gametophyte
  • Homosporous.

Characters:

1) First Land Plants:

The first plants to colonize land were bryophytes.



2) Origin:

They are generally thought to have evolved from green algae.


3) Habitat Adaptation:

The Bryophytes are poorly adapted to life on land and are mainly confined to damp shady places.


4) Non-vascular Plants:

These plants are devoid (lacking in) of specialized conducting (xylem and phloem) and strengthening tissues.


5) Transportation by Diffusion:

Only the process of diffusion helps in the transportation of water minerals as well as in transportation of prepared food and other substances.


6) Cuticle:

The plant body is with a proper cuticle, without cuticle or has a very thin one.

The water is absorbed by the general surface of the plant.


7) Amphibious Plants:

The bryophytes are said to be the amphibians of the plant world because they cannot live away from water.

They need water for reproduction.


8) Non-flowering:

The bryophytes are non-vascular, flowerless plants.


9) Alternation of Generation:

These plants show a regular alternation of heteromorphic (morphologically different) generations.

They have a dominant independent free living gametophyte.


10) Thalloid:

This may be thalloid as in many liverworts or is differentiated into structures resemble with stem, leaves and absorbing and anchoring organs, rhizoids as in mosses and source liverworts.


11) Reproduction:

i. Gametophyte Generation:

The gametophyte produces a sporophyte, which is a less conspicuous generation, partially or totally dependent upon the gametophyte for its nutrition.


ii. Sporophyte Generation:

The sporophyte generally consists of foot, seta and capsule.

The sporophyte is diploid (2n) which produces in sporangia one kind one kind of haploid spores (i.e. it is homosporous) by meiosis.

The spores germinate and give rise to gametophyte which is also haploid.


iii. Sex Organs:

ANTHERIDIA multicellular male sex organs and ARCHEGONIA female sex organs both are born on gametophyte either on same or different plants.


iv. Protection of Sex Cells:

These sex organs are multicellular and protected by a sterile covering of cells.


v. Gametes:

Gametes are produced by Mitosis.


vi. Antherozoid:

Male gametes produced by antheridia are called antherozoid; antherozoids are motile and always produced in large number.


vii. Eggs:

Female gametes formed within archegonia are termed as eggs.

A single egg is formed in each archegonium.


viii. Fertilization:

Fertilization takes place in water.

Antherozoids (n) are towards archegonia (n) Chemotactically.

A single antherozoid fuses with an egg (n) thus accomplishing fertilization which results in the formation of the diploid zygote (2n)


ix. Zygote is Retained with in Archegonium:

The zygote is retained within the female sex organ (archegonium) for some time.


x. Embryo Formation:

After a resting period the zygote develops by mitotic division into a diploid embryo.


xi. Sporophyte Depend on Gametophyte:

The embryo ultimately develops into a sporophyte which is also diploid.

The entire development of sporophyte thus takes place within the gametophyte plant body.

Even when the sporophyte is fully developed it remains attached to the gametophyte for nourishment and protection because it does not contain chloroplast and is unable to perform photosynthesis.


IMPORTANCE OF ALTERNATION OF GENERATION:

There is an alternation of generation in the life cycle of bryophytes i.e. multicellular haploid gametophytic (gamete producing) generation alternates with the multicellular diploid sporophytic (spore producing) generation.

It is a very important phenomenon, which provides continuous genetic variabilities and selection for the best genetic make up for survival and adaptation in the changing environment.




General Characters of Bryophytes General Characters of Bryophytes Reviewed by SaQLaiN HaShMi on 5:39 AM Rating: 5

Differentiation between Acoelomates, Pseudocoelomates and Coelomates.

 Differentiation between Acoelomates, Pseudocoelomates and coelomates.



ACOELOMATES:

Ø  In phylum Platyhelminthes there is no body cavity or coelom, and the mesoderm form a loose, cellular tissue called mesenchyma or parenchyma which fills the space between the ectoderm and endoderm.

Ø  It forms a packing around the internal organs of the animals to support and protect them.

Ø  Such animals are called acoelomates

Ø  In acoelomates the gut is sac-type and there is no special transport system.

Ø  Only excretory system is developed for the transport of excretory products.

This system consists of flame cells, excretory ducts and excretory pores.

Ø  However the nervous system is well developed.


PSEUDOCOELOMATES:

Ø  In Aschelminthes the space between the body wall and the digestive tube is called pseudocoelom (false body cavity)

Ø  Pseudocoelom is not homologous to true coelom because.

Ø  It is not lined by coelomic epithelium.

Ø  It has no relation with the reproductive and excretory organs.

Ø  It develops from the blastocoel of the embryo and it is bonded externally by the muscles and internally by the cuticle of the intestine.

Ø  The animals having pseudocoelom are called pseudocoelomates.


COELOMATES:

Ø  Coelom is cavity present between the body wall and the alimentary canal and is lined by mesoderm.

Ø  The mesoderm splits into outer parietal layer (somatic) which under lines the body wall and the visceral layer (splanchnic) which covers the alimentary canal and the cavity between them is the true coelom.

Ø  It is filled with fluid called coelomic fluid.

Ø  The animals which posses coelom or true body cavity are called coelomates e.g. animals from annelids to chordates.

Ø  In coelomates gut attains more complexity and neuro-sensory system is well developed along with excretory system, circulatory system, respiratory and reproductive system.




Differentiation between Acoelomates, Pseudocoelomates and Coelomates.  Differentiation between Acoelomates, Pseudocoelomates and Coelomates. Reviewed by SaQLaiN HaShMi on 9:58 PM Rating: 5

Test used to detect Lipids

 Test used to detect lipids?


Following tests are used to detect lipids:

(i)    Sudan-III Test: 

Experiment

Observation

Inference

2 ml original solution in test tube + 2 ml water + Few drops of Sudan III + Shake well.

Red stained oil layer separates on surface of water, which remains uncoloured.

Lipid present.

 

(ii)    Emulsion Test:

Experiment

Observation

Inference

2 ml O.S + 2 ml absolute ethanol + Shake well + Equal volume of cold water

Cloudy white suspension is formed.

Lipid present.

 

What are lipids ?

Lipids are the organic compounds made up of carbon, hydrogen and oxygen, are characterized by their solubility in organic solvents such as ether, alcohol and their insolubility in water.

 

Test used to detect Lipids Test used to detect Lipids Reviewed by SaQLaiN HaShMi on 8:37 PM Rating: 5

Lymphatic System, Its Structure and Function

What is the lymphatic system, write down its structure and function?


LYMPHATIC SYSTEM:

Definition:

(That system which consists of tissue fluid its transport and regulates the substances in body)

This system is responsible for the transport and returning of materials from the tissues of the body to the blood.

The system comprises of:

  • Lymph capillaries,
  • Lymph vessels,
  • Lymph nodes, and
  • Lymphoid masses,
  • Lymph-the fluid which flows in the system.

(1) Lymph Capillaries:

Lymph capillaries end blindly in the body tissues, whore pressure from the accumulation of interstitial fluid or extracellular fluid forces the fluid into the lymph capillaries.


(2) Lymph and Lymph Vessels:

When this fluid enters the lymph capillaries, it is called lymph.

The lymph vessels empty in veins;

So lymph is a fluid in transit between interstitial fluid and the blood.

The intercellular spaces in the walls of lymph vessels are larger than those of the capillaries of blood vascular system.

So large molecules, from the interstitial fluid cal also enter the lymph capillaries.


Thoracic Lymph Vessel and Subclavin Vein:

Lymph capillaries join to form larger and larger lymph vessels; and ultimately from thoracic lymph duct-which opens into subclavian vein.


Direction of Flow:

The flow of lymph is always towards the thoracic duct.


Lacteals:

In the intestine, the branches of lymph capillaries, within villi, are called lacteals.

 The flow of lymph is maintained by:

(i) Activity of skeletal muscles,

(ii) Movement of viscera (internal organs)

(iii) Breathing movements.

(iv) Valves, which prevent back flow of lymph.


(3) Lymph Nodes:

Along the pathway, the lymph vessels, have, at certain points, masses of connective tissue where lymphocytes are present, these are lymph nodes. Several afferent lymph vessels enter a lymph node, which is drained by a single, efferent lymph vessel.


Location:

Lymph nodes are present in the:

(i) Neck Region.

(ii) Axilla (armpit) and.

(iii) Groin (genitalia) of humans.


(4) Lymphoid Masses:

In addition, several lymphoid masses are present in the:

(i) Walls of the digestive tract,

(ii) In the Mucosa and Sub-mucosa


The larger masses are:

(i) Spleen

(ii) Thymus

(iii) Tonsils (tissue mass in mouth) and

(iv) Adenoids (throat tissue) are all lymphoid masses.

These produce lymphocytes.



(5) Functions:

These are several functions performed by the lymphatic system.


(i) Regulation of Blood Volume:

In an average person, about three litres more fluid leaves the blood capillaries than is reabsorbed by them each day.

It returns this excess fluid and its dissolved proteins and other substances to the blood.


(ii) Absorption of Lipids:

The lacteals of villi absorb large fat globules, which are released by interstitial cells after the products of digestion of fats are absorbed.


(iii) Defence Mechanism:

The lymphatic system helps defend the body against foreign invaders.

Lymph nodes have lymphocytes and macrophages that destroy the bacteria and viruses.

The painful swelling of lymph nodes in certain diseases (mumps is an extreme example) is largely a result of the accumulation of dead lymphocytes and macrophages.


(iv) Filtering Blood Destroyed aged RBC and Invaders:

Just as the lymph nodes filter lymph, the spleen filters blood, exposing it to macrophages and lymphocytes that destroy foreign particles and aged red blood cells.

Lymphatic System, Its Structure and Function Lymphatic System, Its Structure and Function Reviewed by SaQLaiN HaShMi on 6:54 AM Rating: 5

A short note on Chemiosmosis

 A short note on Chemiosmosis


CHEMIOSMOSIS:

In both cyclic and non-cyclic phosphorylation, the mechanism for ATP synthesis is chemiosmosis, the process that uses membranes to couple redox reactions to ATP production.


(1) Pumps Protons (H+):

Electron transport chain pumps protons (H+) across the membrane of thylakoids in case of photosynthesis into the thylakoids space.

They energy used for this pumping comes from the electrons moving through the electron transport chain.


(2) Potential Energy:

This energy is transformed into potential energy stored in the form of H+ gradient across the membrane.


(3) ATP Synthase:

Next the hydrogen ions move down their gradient through special complexes called ATP synthase which are built in the thylakoid membrane.

During this diffusion of electrons, the energy of electrons is used to make ATP




A short note on Chemiosmosis  A short note on Chemiosmosis Reviewed by SaQLaiN HaShMi on 9:29 PM Rating: 5

The Mechanism of Opening and Closing of Stomata

OPENING AND CLOSING OF STOMATA:


The guard cells function as multisensory hydraulic valves.

Environmental Factors:

Environmental factors such as:

(i) Light intensity and quality.

(ii) Temperature.

(iii) Relative humidity and

(iv) Intracellular CO2 concentration are sensed by guard cells and these signals are integrated (combine) into well-defined stomatal responses.


These are two hypothesis which may explain the opening and closing of stomata.

(1) Starch Sugar Hypothesis:

The German Botanist H. Van Mohl proposed that the guard cells are the only photosynthesising cells of epidermis of leaf.

Sugar are produced in the guard cells during day time when light is available.

(i) During Day Time:

When sugar level rises i.e. solute concentration increases or water potential decreases and the guard cells become turgid, and they separate from one another and stoma or pore opens.

(ii) During Night:

During night there is no photosynthesis the sugars are either converted into in soluble starch or are used in respiration, this decreases free sugars in cell.

So the osmotic pressure of guard cells is lowered, and water leaves the guard cells. They become flaccid and stoma or pore between them closes.

But these process are not fast enough to account for the rapid rise in turgor, of guard cells.

(2) Influx of Kᐩ Ions:

Potassium concentration in guard cells increases several folds,

Depending upon plant species.

(i) Stomata Open:

Stomata open due to active transport of potassium ions (Kᐩ) into the guard cells from the surrounding epidermis.

The accumulation of Kᐩ decreases the osmotic potential of guard cells.

Water enters the guard cells by osmosis, which become more turgid and stretched and stomata are opened.

(ii) Stoma Closes:

The stoma closes by reverse process; involving passive diffusion of K⁤ᐩ from guard cells followed by water moving out by osmosis.


What Controls the Movement of Kᐩ into and out of Guard Cells ?

  • Level of carbon dioxide in the spaces inside the leaf end.
  • Light, control this environment.

(i) Level of Carbon Dioxide:

A low level of carbon dioxide favors opening of the stomata, thus allowing an increased carbon dioxide level and increased rate of photosynthesis.

(ii) Light Quality and Intensity:

Exposure to blue light, which is also effective in photosynthesis has been shown to acidify the environment of the guard cells (i.e. pumps out protons) which enable the guard cells to take up Kᐩ followed by water uptakes resulting in increased turgidity of guard cells.

So in general stoma are open during day and closed at night.

This prevents needless loss of water by the plant when it is too dark for photosynthesis.

(iii) Actively Pumping Potassium:

The plant open their stomata by actively pumping potassium in guard cells causing water to follow by osmosis.

Guard cells become turgid and stoma or pore opens.

When Potassium leaves the guard cells (during night) water leaves the guard cells by exosmosis and guard cells become flaccid and stoma or pore between guard cells closes.

The Mechanism of Opening and Closing of Stomata The Mechanism of Opening and Closing of Stomata Reviewed by SaQLaiN HaShMi on 5:53 AM Rating: 5

The Mechanism of Phloem Translocation or pressure flow


THE MECHANISM OF PHLOEM TRANSLOCATION:


Pressure-Flow Theory:

The theory called, Pressure-Flow Theory, is the most acceptable theory for the transport in the phloem of angiosperms.

Evidence to Support this Theory:

We have considerable evidence to support this theory.

Two Categories:

There were two main categories of theories to account for movement of sap in phloem.

(i)   Active Theories:

The Active theories involving the use of energy for the movement of materials in phloem.

(ii)   Passive Theories:

The passive theories in which no use of energy was involved. The active theories have all been abandoned (alone, with out support) as there is not much evidence to support these theories.

Now we are left with Passive theories of transport/translation.

These Include:

(i) Diffusion

(ii) Pressure flow theory

(i)  Diffusion:

Diffusion is far too slow, to account for the velocities of sugar movement in phloem, which on the average is 1 meter per hour, while the rate of diffusion is 1 meter per eight years.

So we are left with pressure flow theory.

Pressure Flow Theory:

A hypothesis was first proposed by Ernst Munch in 1930.

It states that the flow of solution in the sieve elements is driven by an osmotically generated pressure gradient between source and sink.

Now this hypothesis has been given status of a theory.

See figure, the following steps, explain pressure flow theory.

(i) The glucose formed in the photosynthesizing cells, is used within the cell (for respiration etc) and the rest is converted in to non-reducing sugar i.e., sucrose.

(ii) This source is actively transported through the bundle sheath cells to the companion cell of the smallest vein in leaf a short distance transport (involving 2-3 cells).

Thus sucrose diffuses through plasmodesmata to sieve tube cell or sieve element, raising the concentration of sucrose in it.

The pathway taken by sucrose is symplast in most cases; but in some, apoplastic movement does take place.

The sucrose is actively transported to the sieve elements.

(iii) The water moves by osmosis from the nearby xylem in the leaf vein.

This increase the hydrostatic pressure of the sieve tube element.

(iv) Hydrostatic pressure moves the sucrose and other substances in the sieve tube cells, and moves to sinks e.g. fruits.

In the storage sinks, such as sugar beet root and sugarcane stem, sucrose is removed into apoplast prior to entering symplast of the sink.

(v) Water moves out of the sieve tube cell by osmosis, lowering the hydrostatic pressure.

In symplastic, pathway sucrose (or sugars) moves through plasmodesmata to the receiver cell.

Thus according to pressure flow theory, the pressure gradient is established as a consequence of entry of sugars in the sieve elements at the source; and removal of sugars (sucrose) at the sink

The energy driven energy of sugars in sieve tube elements, generate high osmotic pressure in the sieve tube elements of the source causing a steep drop in the water potential.

(vi) The pressure of sieve plants greatly increase the resistance along the pathway and results in the generation and maintenance of a substantial (considerable) pressure gradient in the sieve elements between source and sink.

The sieve element's contents are physically pushed along the transportation pathway by bulk flow, much like water flowing through a garden hose.

The pressure flow theory accounts for the mass flow of molecules within phloem.

It may be noted that the photosynthate or carbohydrates from the mesophyll cells to phloem tissue involves diffusion and active transport (carrier mediated transport).

Then in phloem tissue (sieve tubes) the movement of materials is according to pressure flow theory.

Again in the sink cells when the sugar and the carbohydrates are passed from the phloem tissue, diffusion and carrier mediated transport, either passive or active, takes place.

The Mechanism of Phloem Translocation or pressure flow The Mechanism of Phloem Translocation or pressure flow Reviewed by SaQLaiN HaShMi on 8:17 AM Rating: 5

Aiou past papers MSc Botany 4th Semester

12:54 AM
Aiou past papers MSc Botany 4th Semester Aiou past papers MSc Botany 4th Semester Reviewed by SaQLaiN HaShMi on 12:54 AM Rating: 5

Aiou past papers MSc Botany 2nd Semster

11:54 PM
Aiou past papers MSc Botany 2nd Semster Aiou past papers MSc Botany 2nd Semster Reviewed by SaQLaiN HaShMi on 11:54 PM Rating: 5
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