Basics of Biology

Phylum Protozoa

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Table of Content
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➤Protozoa- Definition, characteristics, classification, examples

➤ Economic importance of protozoans

GENETICS

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GENETICS

👉DNA: A Genetic Material

👉Griffith's Experiment

👉Hershey-Chase experiment

Class 10 life processes important questions

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1. What are enzymes? Name any one enzyme of our digestive system and write its function.

Answer. Enzymes are biological catalysts. Catalysts are proteins that increase the rate of chemical reactions without being used up.

For example: Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine

2. (i) Write the balanced chemical equation for the process of photosynthesis,

Answer.

Photosynthesis can be represented using a chemical equation. The overall balanced equation is

6CO₂ + 12H₂O ^Sunlight C₆H₁₂O₆+ 6H₂0 + 6O₂

(ii) When do the desert plants take up carbon dioxide and perform photosynthesis?

Answer.

Desert plants open up their stomata during night and take in CO₂. Stomata remains close during the day time to prevent the loss of water by transpiration. They store the CO₂ in their cells until the sun comes out and they can carry on with photosynthesis during the day time.

3. In single celled organisms diffusion is sufficient to meet all their requirements of food, exchange of gases or removal of wastes but it is not in case of multicellular organisms. Explain the reason for this difference.

Answer.

Unicellular organisms can absorb sufficient oxygen because of its complete contact with the atmosphere, but in multicellular organisms the rate of absorption and diffusion becomes very less because all cells are not in direct contact with the atmosphere. Multicellular organisms require greater amount of oxygen to sustain life processes which cannot be fulfilled by the process of diffusion.

4. Name the acid presents in the following:

(i) Tomato (ii) Vinegar (iii) Tamarind Answer.

(i) Oxalic acid: Oxalic acid is an organic compound found in many plants. These include leafy greens, vegetables, fruits, cocoa, nuts and seeds

(ii) Citric acid: Citric acid is found naturally in citrus fruits, especially lemons and limes. It's what gives them their tart, sour taste.

(iii) Tartaric acid: Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus.

5. State the role of the following in human digestive system:

(i) Digestive enzymes (ii) Hydrochloric acid (iii) Villi Answer.

(i) Digestive enzymes – Foods need to be broken into their small or simpler molecules so that they can be absorbed into the bloodstream. However, the physical breakdown of food is not enough. Enzymes are hence needed for the chemical breakdown of food and speeding up the digestive process. The products of digestion can hence be small enough to be absorbed.

(ii) Hydrochloric acid – Hydro chloric acid helps to kill the germs which might have entered in to the system through food. It creates acidic medium for the pepsin to act on food to breakdown proteins.

(iii) Villi – Villi are finger like projections in the small intestine. They help to increase the surface area for absorption of the digested food. Villi are richly supplied with blood vessel which help to absorb digested food in to the blood stream.

6. (a) Explain how does the exchange of gases occur in plants across the surface of stems, roots and leaves.

Answer

(a) In plants there are tiny pores called stomata on leaves and lenticels in stem which facilitate the exchange of gases. Carbon dioxide is taken in and oxygen given out {during photosynthesis} and vice versa during respiration.

(b) How are water and minerals transported in plants?

Answer

(b) Water and minerals are transported within the plant by the Xylem vessels (mainly in an upward direction); these are part of the vascular system which also includes Phloem vessels.

Phloem transports the products of photosynthesis within the plant, to all parts like the stem, roots, fruits etc. in all directions.

7. Mention the raw materials required for photosynthesis.

Answer.

The following raw materials are required for photosynthesis:

(i) Carbon Dioxide: Plants get CO₂ from atmosphere through stomata.

(ii)Water: Plants absorb water from soil through roots and transport to leaves.

(iii) Sunlight: Sunlight, which is absorbed by the chlorophyll and other green parts of the plant.

8. Why do herbivores have longer, small intestine than carnivores?

Answer.

Digestion of cellulose takes a longer time. Hence, herbivores eating grass need a longer small intestine to allow complete digestion of cellulose. Carnivorous animals cannot digest cellulose due to the absence of enzyme CELLULASE, hence they have a shorter intestine.

9. Write correct sequence of four steps of method for the preparation of temporary mount of a stained leaf peel.

Answer.

Take a healthy leaf from the potted plant.

1. Remove a part of the peel from the lower surface of the leaf. You can do this by folding the leaf over and gently pulling the peel apart using forceps.

Keeps the peel in a watch glass containing water.

2. Put a few drops of safranin stain in a watch glass.

3. After 2-3 minutes take out the peel and place it on a clean glass slide.

4. Put a drop of glycerin over the peel and place a clean covers lip gently over it with the help of a needle.

5. Remove the excess stain and glycerin with the help of blotting paper.

6. Observe the slide under magnifications of the compound microscope.

Circadian Clock in Mice controls by Sodium, New Study Reveals.

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Circadian Clock in Mice controls by Sodium, New Study Reveals.

A new research published this week in the journal Nature shows that injection of salt mice (hypertonic saline) leads to activation of neurons in the suprachiasmatic nucleus, the circadian master clock for the brain.

Our circadian clock or circadian rhythm adapts the cells and organs of our body at various times of the day to change requirements.

Circadian rhythm disturbance due to jetlag or shift work may cause negative health consequences.

Light the primary factor that regulates our circadian clock is clearly defined, it was unclear whether or how physiological factors could regulate the suprachiasmatic nucleus.

"With our analysis we are the first to show that the physiological signals in the suprachiasmatic heart can actually control clock times," said Professor Charles Bourque, a researcher at the McGill University Health Center's research center.

Professor Bourque and PhD student Claire Gizowski of McGill University were shown to be able to activate the circadian clock at a time of day when it is normally quiet, with salt sensitive neurons located in one particular region of the brain — the organum vasculosum of the lamina terminalis.

"This means we can speed up the clock, which may be helpful to adapt faster to the time change linked to long-term travel, or if the schedule of our work is shift by several hours," said Gizowski.

The scientists now hope to determine whether or not natural increases in blood sodium – through eating – have the same effect and are occurring in humans.

"One problem is that, while it is good and not dangerous to ingest small quantities of salt, it is poisonous when ingested in large quantities," said Bourque.

"There is far further research required to evaluate whether this result is healthy and realistic for humans."

C. Gizowski & C.W. Bourque. Sodium regulates clock time and output via an excitatory GABAergic pathway. Nature, published online July 8, 2020; doi: 10.1038/s41586-020-2471-x

Define Life Processes Class 10

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What are life processes ??

The maintenance functions of living organism must go on even when they are not doing anything particular. Even when we are just sitting in class, even we are just asleep; this maintenance job has to go on. The processes which together perform this maintenance job our life processes.

Since these maintenance processes are needed to prevent damage and break-down, energy is needed for them. This energy comes from outside the body of the individual organism. So there must be a process to transfer a source of energy from outside the body of the organism, which we called food, to the inside, a process we commonly called nutrition. If the body size of the organism is to grow, additional raw material will also be needed from outside. Since life on earth depends on carbon-based. molecules, most of these food sources are also carbon-based. Depending on the complexity of these carbon sources different organisms can then use different kinds of nutritional processes.

The outside source of energy could be quite varied, since the environment is not under the control of the individual organism. These source of energy therefore, need to be broken down or build up in the body, and must be finally converted to a uniform source of energy that can be used for various molecular movements needed for maintaining living structures, as well as to the kind of molecules the body needs to grow. For this, a series of chemical reactions in the body are necessary. Oxidising and reducing reactions are some of the most common chemical means to break down molecules. For this, many organisms use oxygen source from outside the body. The process of acquiring oxygen from outside the body, and to use it in the process of breakdown of food sources for cellular needs, is what we called respiration.

In the case of single celled organisms, no specific organs for taking in food. Exchange of gases or removal of waste may be made because the entire surface of the organism is in contact with the environment. But what happens when the body size of the organism increases and the body design becomes more complex?

In multicellular organisms, all the cells may not be in direct contact with the surrounding environment. The simple diffusion will not meet the requirements of all the cells.

We have seen previously how, in multicellular organisms, various body parts have specialised in functions they perform. We are familiar with the idea of these specialised issues, and with their Organisation in the body of the organism. It is therefore not surprising that the uptake of food and of oxygen will also be the function of the specialised tissues. However, this poses a problem, since the food and oxygen are Now taken up at one place in the body of the organisms, while all the parts of the body need them this situation create a need for a transportation system for carrying food and oxygen from one place to another in the body.

When chemical reactions use the carbon source and the oxygen for energy generation, they create by-products that are not only useless for the cells of the body, but could even be harmful. These waste by-products are therefore needed to remove from the body and discarded it outside by the process called excretion. Again if the basic rule for body design in multicellular organisms are followed, a specialised tissue for excretion will be developed which means that the transportation system will need to transport waste away from cells to its excretory tissue.

Let us considered these various processes are essential to maintain life one by one

Larval forms of Echinoderms……..

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Larval forms of Echinoderms……..

A. Dipleurula Larva:

1. The dipleurula form is reached during development and is characterised by its bilaterally symmetrical, egg-shaped body.

2. The ventral concave side bears the mouth and is encircled by a circumoral ciliated band.

3. The digestive canal is differentiated into oesophagus, stomach and intestine while anus is disposed ventrally.

4. The pre-oral lobe which is situated at the anterior to mouth, bears an apical sensory plate and a tuft of cilia.

5. The ciliation on the surface of the body becomes reduced to a ciliard band.

>>>This Dipleurula form is regarded by many as the hypothetical ancestral form of Echinoderm, as this form is universally present. The Dipleurula concept was first propounded by Bather (1900). The major changes involved in other Echinoderm larvae are due to differential disposition of the ciliated bands.

B. Pentactula Larva:

1. The Pentactula larva has five tentacles around the mouth.

2. The hydrocoel is separated from the rest of the coelom to form the future warer vascular system.

>>> This larval stage is regarded as the next evolutionary step of the Dipleurula larva. This concept has been supported by Semon (1888), Burry (1895), Hyman (1955) and many others.

C. Bipinnaria Larva:

1. It is a bilaterally symmetrical free swimming pelagic larva ; the anterior end of the archenteron develops as mouth and blastopore becomes the anus.

2. It possesses two ciliated bands—the pre-oral and the post-oral.

3. The pre-oral ciliated band surrounds the pre-oral lobe of the larva.

4. The pre-oral lobe is highly developed.

5. The post-oral ciliated band appears to be longitudinally placed and forms a complete ring between the mouth and anus.

6. The pre-oral and post-oral ciliated bands are continued over a series of prolongations of the body, called arms.

7. The name and number of the arms developing from pre-oral and post- oral ciliated bands are as follows:

8. The pre-oral and ventro-median arms develop from the pre-oral ciliated band and the rest of the arms develop from the post-oral ciliated band.

>>> The bipinnaria is a feeding larva and leads a free-swimming life. After a short period of free-swimming existence it transforms into a lecithotrophic brachiolaria larva.

D. Brachiolaria Larva:

1. This type of larva is present in Asteroidea and is regarded as a modified form of bipinnaria larva. It possesses the following special features.

2. There are three additional arms which are not ciliated in their courses except in Bipinnaria papillata. These arms are called the brachiolar arms and are beset with warts to help in temporary adhesion.

3. These arms are devoid of calcareous rods and have prolongations from the coelomic cavity.

>>> The bipinnaria stage is followed by the brachiolaria stage in all Asteroids but direct evidence is only furnished in two cases, e.g., Asterias glacialis and A. vulgaris. In Astropecten the brachiolaria stage is absent and the bipinnaria larva metamorphoses directly into adults.

E. Auricularia Larva:

1. A free-swimming form.

2. Body barrel-shaped and bilaterally symmetrical.

3. The preoral lobe is well formed.

4. A single winding ciliated band, which may be produced into lobes.

5. Gut with mouth, sacciform stomach, hydrocoel and right and left stomocoels and anus.

6. The hydrocoel becomes lobulated forming primary tentacles and communicates with the hydropore by a canal.

7. Calcareous rods replaced by spheroid or star-shaped or wheel-like bodies.

>>> The auricularia larva is transformed into a Doliolaria larva similar to that of Crinoidea.

F. Doliolaria Larva:

1. A free-swimming form.

2. Body barrel-shaped and bilaterally symmetrical.

3. Preoral lobe well-developed.

4. Wavy, continuous band break into 3-5 flagellated, transverse rings.

5. The auricularia larva transforms into a barrel-like body with five ciliated bands which subsequently break into pieces. This particular stage is also designated as pupa stage.

6. During metamorphosis into an adult form, the ciliated bands disappear and further changes occur.

G. Pluteus Larva:

1. This larval form can be regarded as a modification of the auricularia larva.

2. Like the auricularia larva it has a single ciliated band, but it possesses long arms with ciliated bands at the margin.

3. It has comparatively smaller pre-oral lobe.

4. The post-anal part of the body is quite well-developed.

5. The arms are also supported by calcareous rods.

The pluteus larvae are of two kinds:

(1) Ophiopluteus—in Ophiuroidea.

(2) Echinopluteus—in Echinoidea.

>>> Both the larval forms possess the post-oral arms, antero-lateral arms, postero-lateral arms and postero-dorsal arms.

(1) Ophiopluteus

1. Free-swimming.

2. Arms are four pairs, slender and supported by calcareous skeleton.

3. Posterolateral arms are longest and directed forward, giving the larva V-shaped appearance.

4. Ciliated bands are present on the edges of arms.

5. The alimentary canal is divisible into mouth, oesophagus, stomach and intestine opening through the anus.

(2) Echinopluteus—in Echinoidea.

1. Free-swimming.

2. Arms five or six pairs, pigmented and supported by calcareous skeleton.

3. The posterolateral arms are very short and directed outward or backward.

4. The skeletal rods simple or thorny or fenestrated or branched.

5. The zones of the alimentary canal are mouth, oesophagus, stomach and intestine opening through the anus.

H. Antedon or Yolk Larva:

1. This particular larva is also called doliolaria larva or Vitellaria larva.

2. This larval stage is present in Antedon and it has many structural pecularities.

3. It has a barrel-shaped body with slightly flattened ventral side.

4. It is free-swimming and exhibits bilateral symmetry.

5. The ciliated bands are in the form of four or five separate transversely placed bands encircling the body. In Antedon bifida, there are four bands. In Antedon adriatica and A. mediterranea there are five bands.

6. A tuft of cilia with stiff sensory hair springs from a thickened ectodermal patch, called apical neural plate, which is comparable to that of Tonaria larva of Balanoglossus.

7. The anterior ciliated ring is ventrally incomplete.

8. There is a ciliated depression or larval mouth which is ventrally placed between the second and third ciliated rings.

9. A small adhesive pit develops between the first and second ciliated rings by which the larva adheres to the substratum.

10. The internal structures become rotated at an angle of 90° from the ventral to the posterior side.

I. Cystidean or Pentacrinoid Larva:

1. The anterior end of the antedon larva, after attachment, is prolonged into an elongated narrow stalk and the free end becomes broader.

2. The ciliated depression becomes a closed ectodermal vesicle which is gradually shifted to the free end.

3. The floor of the depression is perforated by mouth and with the disappearance of the roof; the mouth and the tentacles become exposed.

4. This particular phase is called Cystidean or Pentacrinoid stage. This stage resembles closely the adult Pentacrinus. The stalk in this form develops from the pre-oral lobe.

Inborn error of Metabolism; Alkaptonuria and Phenylketonuria by video lecture

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How metabolism problems comes from parents ??

Watch this video for better understand

Water Vascular or Ambulacral System of Star Fish ; Asterias

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how start fishes moves without fins??????

let see how ⇊⇊⇊

Water Vascular or Ambulacral System

Water Vascular System is a unique feature of of all the echinoderms which helps mainly in locomotion.

This it is the modified part of the coelom and consists of a system canals which is filled with sea water, containing amoeboid corpuscles.

It plays a vital role in the· locomotion of the animal and obtaining food is the major function of water Vascular system.

The water vascular system of starfish consists of

1. madreporite,

2. stone canal,

3. ring canal,

4. radial canal,

5. Tiedemann’s bodies,

6. polian vesicles,

7. lateral canals and

8. tube feet.

1. Madreporite

The water vascular system of star fish starts from the madreporite, which is rounded and hard due to calcareous plate on the aboral surface of the central disc of the body.

Figure 1.

Its surface bears numerous fines radiating grooves or furrows, having at their bottom minute ciliated pores.

Each furrow contains as many as 200 to 250 pores, which lead into very short and fine tubes called the pore canals as shown in Figure 1 above.

Each pore canal unite to form larger collecting canal called ampulla of stone canal as shown in Figure 1 above.

2. Stone Canal:

Stone canal is a 'S' shaped tube opening on the oral side into a ring canal around the mouth.
Its wall is supported by series calcareous rings hence called 'stone canal.

Figure 3.

The lumen of the stone canal is lined by ciliated cells which draw the water current into canal.

The wall of the stone canal projects into its cavity like ridge that bifurcates into lamellae.

Stone canal along with an axial organ is enclosed in a coelomic sac called axial sinus.

The stone canal, axial organ and axial sinus these three together form the axial complex as shown in figure 4.

Figure 4.

3. Ring Canal:

It is wide, slightly pentagonal ring which forming round the oesophagus.
Angles of pentagon lies in the radial canal.
From outer surface of canal it gives off 5 radial canals entering in each arm.
The radial canal runs up to the tip of each arm.

Figure 5.

4. Radial Canal

The radial canals carry water from ring canal and distribute to Ampullae; which have a tube feet theough which the water moves.

Figure 6.

5. Tiedemann's Bodies:

These are also known as racemose gland. They are of 5 pairs.

On the inner side of ring canal its gives off small irregularly shaped bodies which are known as the tiedemann's bodies.

There are 9 Tiedemann's bodies 1 is absent from where stone canal arises as shown in figure 7. below.

The function of these bodies is to produce coelomic corpuscles which are released into the ring canal and so the system is known as water vascular system.

Figure 7.

6. Polian Vesicles:

Figure 8.

Polian vesicles are large, thin walled, pear shaped sac.

In each inter radius of the ring canal it gives off 2 to 4 Polian vesicles.

They act as contractile structures which mainly store s water.

The main function of these vesicles are found to regulate the pressure in water vascular system.

These vesicles also helps in manufacture amoeboid cells.

7. Lateral Canals

Each radial canal, arises two series of narrow lateral canals in each arm, along its entire length.
Each lateral canal opens into a tube foot, the opening is guarded by a valve which prevent back flow of fluid into radial canal.

Figure 9.

8. Tube Feet:

The tube feet are arranged in grooves along the arms.
They operate through hydraulic pressure.
They are used to pass food to the oral mouth at the center, and can attach to surfaces.
Each tube foot can be distinguished into three regions, a rounded sac-like ampulla, a middle tubular podium and a cup like sucker at the lower end.

Function:

The tube feet are locomotory and respiratory in function.

They also help in attaching the body to the substratum and in capturing and handling the food.

Ask any doubt in comment section below.............

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Subscribe for more lectures ...............😇

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Examples of Multiple Allelism

2020-04-12T00:54:00.000+05:30

Gene may has more than 2 alleles 😕....
Is it !!!!!!!!

As we have studied that some genes may exist in three or more allelic forms which we called as multiple alleles. ⇦

Here are some examples of multiple allelism

ABO Blood group in Humans.
Skin Colour in Humans.
Eye colour in Drosophila.
Coat colour in Rabbit.

1. ABO Blood group in Humans.

A classical example of multiple alleles is found in the ABO blood group system of humans.

The RBC's of people with type A blood group contain A antigens, those with blood group B contain B antigens, those with type AB blood group have both A and B antigens and those with O blood group don't have any A or B antigens.

The IA and IB  alleles are responsible for production of A and B antigens.

The alleles IA for the A antigen is codominant with the allele IB  for the B antigens.

Both IA and IB are completely dominant to allele i, which fails to specify A or B antigens.

The plasma of type A blood contain anti-B antibodies, type B blood contains anti-A antibodies, no anti-A and anti-B antibodies are present in type AB blood, and both anti-A and anti-B antibodies are present in type O blood.

Table 1. Human ABO blood group

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2. Eye colour in Drosophila

Drosophila eye colour is red normally which is coded by a wild type allele.

1st mutation observed in red eye gene to become white eyed Drosophila (mutant type)

After while different shades between red and white were observed. About a dozens of allelomorphs some are showing below in table 2.

red eye is dominant over the other.

When any of the two recessive alleles crossed the intermediate eye colour was observed.

now the question arise how is this white eyed phenotype inherited?

lets have a look ..........

We have a flies with white eyes and that white eyed flies come after the mutation in a gene which is responsible for red eye colour of flies..

First... the parental cross

From all the red eyed flies in F1 generation, we revealed that white eyed phenotype is recessive.

We can say that in white eyed flies there may be a mutation in red colour dominant allele which may result from failure to produce red colour eye.

now...
take one of F1 progeny & lets do test cross.......

4 different phenotypes

normally a single gene would give us 2 classes of phenotypes

but here ...

after a test cross we got 4 different phenotypes roughly equal in number
and from these 4 different phenotypes we observed that there must at least 2 genes involved here .

lets understand in more simple way

assume 4 allele control eye colour of Drosophila i.e.

E1 = Wild

E2 = Apricot

E3 = Honey

E4 = White

----E1 > E2 > E3 > E4----

Phenotypes Genotypes

Wildtype E1E1, E1E2, E1E3, E1E4

Honey E2E2, E2E3, E2E4

Apricot E3E3, E3E4

White E4E4

Now predict the phenotypic outcome if honey coloured heterozygous fly is crossed with white eyed eyed.

What are the possible phenotypes of the parents in a cross which produces the following offsprings ???

⇑ ⇑
Answer Answer

Multiple Allelism

2020-04-11T17:37:00.000+05:30

Multiple Alleles

As each gene may exist in alternative forms known as alleles, which code for different versions of a particular inherited character.

A part from that some genes may exist in three or more allelic which may be called as multiple alleles.

It is important to note that while multiple alleles occur and are maintained within a population, any individual possesses only two such alleles (at equivalent loci on homologous chromosomes).

Characteristics of Multiple allelism

A single gene has more than 2 alleles.
Only 1 allele of a particular gene occupied by a gamete or a chromosome.
Various alleles of the same gene express different alternative of same trait.
Multiple alleles in a homologous chromosome occupy the similar locus.

Examples of Multiple Allelism

ABO Blood group in Humans.
Skin Colour.
Eye colour in Drosophila.
Coat colour in Rabbit.

Allele definition biology || NEET | AIIMS ||

2020-04-11T15:31:00.002+05:30

Alleles

Each gene may exist in alternative forms known as alleles, which code for different versions of a particular inherited character.

We may also define alleles as genes occupying corresponding positions on homologous chromosomes and controlling the same characteristic (e.g. height of plant) but producing different effects (tall or short).

The term homologous refers to chromosomes that carry the same set of genes in the same sequence, although they may not necessarily carry identical alleles of each gene.

Wild-type Alleles

Normal or Prevalent alleles in a population are called wild-type alleles.

These alleles typically encode proteins that are made in the right amount and function normally.

Mutant Alleles

Alleles that are present at less than 1% in the population and have been altered by mutation are called mutant alleles.

Such alleles usually result in a reduction in the amount or function of the wild-type protein and are most often inherited in a recessive fashion.

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Dominant Alleles

A dominant allele masks or hides expression of a recessive allele and it is represented by an uppercase letter.

Recessive Alleles

A recessive allele is an allele that exerts its effect only in the homozygous state and in heterozygous condition its expression is masked by a dominant allele. It is represented by a lowercase letter.

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Star fish, Asterias: A Type study (P-1)

2020-04-10T00:26:00.003+05:30

Star fish, Asterias: A Type study

In this Part-1 we will study about

1. Taxonomic position

2. Habitat

3. Habits

4. External characters

a) Shape

b) Size

c) Colour

5. Oral or lower or actinal surface

a) Mouth

b) Ambulacral Grooves

c) Podia or Tube feet

d) Eyes and Tentacles

6. Aboral surface

a) Tubercles or Spines

b) Dermal branchiae or Papulae

c) Madreporite

d) Pedicellariae

1. Taxonomic position

Phylum : Echinodermata

Sub phylum : Asterozo

Class : Asteroidea

Order : Forcipulata

Genus : Asterias

Species : rubiens

2. Habitat

Sea-stars are exclusively free living marine animals.
It is found in all oceans at all depths and more abundant in the rocky patches of the shores.
They can be seen partially embedded in the sand immediately often a high tides. They live at the bottom.

3.Habits

· Sea star are nocturnal and carnivorous feed mainly on crustaceans, polychaetes and molluscs.

· The common food of star fish are bivalves.

· They creep slowly along the sea bottom with the help of tube feet or podia.

· Sea star exhibit remarkable power of autonomy (cells or a tissue which is independent on neighbour cells during development) and regeneration.

· They are dioecious and fertilization is mainly external.

· Development is always indirect and include two larvas i.e. Bipinnaria and Brachiolaria

4. External characters

a) Shape

· The body of star fish is oral-aborally compressed.

· It forms a central disc from where five arms will project.

· The arms are broad from the proximally while free at the distal end.

· The arms occupy the radial axis.

b) Size

· The smallest star fish is one cm in diameter, whereas the largest one is 200 cm in diameter.

· The average size varies from 10 to 20 cm.

c) Colour

· Star fish show variety of colours.

· This may show combination of colours and common colours are yellow, orange and brown.

5. Oral or lower or actinal surface

Flat lower surface of the body which is kept towards the substratum. The oral or ventral surface bears following structures

a) Mouth

Central disc of oral surface bears a centrally located opening called as the actinostome or mouth.
It is a pentagonal aperture (two ; 1 and 2 shown in figure below) with five angles, each directed towards an arm.
The mouth is surrounded by a soft and delicate membrane called peristomial membrane or peristome, and is guarded by five groups of oral spines or mouth papillae.

b) Ambulacral Grooves

From each angle of mouth extends out five narrow grooves called ambulacral grooves.
Each groove shows two rows of short tubular retractile projections called tube feet or podia.
Each groove guarded on each side by two or three rows of movable calcareous spines.

c) Podia or Tube feet

Each ambulacral groove contain two rows of short, soft, thin walled, tubular structure called tube feet or podia that end in sucker. Tube feet consist of three parts, ampulla, podium and sucker. Sucker work as suction for the firm attachment on the surface to which it is applied. Tube feet are characteristic organs of echinoderms.

Function:

They are mainly used for locomotion and capturing of food. They are also help in respiration.

d) Eyes and Tentacles

Tip of each arm bears a small median, non-retractile and hollow projection, called terminal tentacle.

It acts as a tactile and olfactory organ. At its base occurs a bright red light sensitive eye spot contains several ocelli.

D. 6. Aboral surface

It is the upper convex dorsal surface is called abactinal surface bears following structures

a) Tubercles or Spines

The entire aboral surface bears by short stout immovable blunt calcareous irregular arranged spines.

b) Dermal branchiae or Papulae

It bears a large number of pores are present between the ossicles of body wall.
Through each pore projects out a very small soft, minute, finger like, hallow retractile process called dermal branchiae or papulae.
Each Dermal branchiae or Papulae is a hallow process of the body wall containing extension of the coelom.
It is respiratory and excretory in function

c) Madreporite

The aboral surface of starfish bears distinct, flat, circular area and conspicuous button like structure called madreporite.
It is located eccentrically on the aboral surface.
It is present in an interradius between two arms, these two arms are called the bivium and the remaining three arms are called trivium.

Anus

A minute circular aperture, the anus is situated close to the centre on the aboral surface of central disc. Echinoderms are the only animals that have an anus in a dorsal position.

d) Pedicellariae

The pedicellariae of starfish are minute, whitish like structures, found on both oral and aboral surfaces of the body, in association with spines.
Pedicellariae are modified spines and microscopic jaw like bodies.
Each consists of a short fleshy and a movable stalk, bearing two articulating calcareous blades or valves, resting upon and articulating with a third calcareous plate, the basal or basilar piece.
According to disposition of valves, two types of pedicellariae occur in Asterias.

1. Straight type

In this type of pedicellariae the two valves are straight and when closed, these meet together along their entire length like a forceps.
Valves open and close with the help of two pair of adductor muscles and one pairs of abductor muscle, respectively.

2. Crossed type

In this type of pedicellariae the two valves cross each other like a pair of scissors.
Straight type occurs largely among the dermal branchiae, whereas the crossed type occurs in cluster at the bases of the spines.
Valves open and close with the help of three pair of adductor muscles and one pairs of abductor muscles, respectively.

Function

The pedicellariae help in the capture and removal of debris and minute organisms, which may settle on the body surface and interfere with respiration by covering the dermal branchiae and tube feet.
In some starfishes, the pedicellariae may help in capturing of small prey.

Aristotle Lantern in Echinoderms

2020-04-03T12:58:00.000+05:30

What Is Aristotle's Lantern?

Our seas are filled with popular creatures – as well as those that are lesser known. This includes creatures and their unique body parts. One of them that has a unique body part and name are sea urchins. The term Aristotle's lantern refers to the mouth of sea urchins. Some people say, however, that it does not solely refer to the mouth alone, but the entire animal.

Where Did the Name Aristotle's Lantern Come From?

It's a funky name for a marine creature body part. This structure was named for Aristotle, a Greek philosopher, scientist and teacher who described the structure in his book Historia Animalium, or The History of Animals. In this book, he referred to the "mouth-apparatus" of the urchin as looking like a "horn lantern." Horn lanterns at the time were five-sided lanterns made up of panes of thin pieces of horn.

Horn lantern

The horn was thin enough for light to shine out, but strong enough to protect a candle from the wind. Later, scientists referred to the urchin's mouth structure as Aristotle's lantern, and the name has stuck thousands of years later.

This complex structure is composed of five triangular, pointed teeth which function in grinding and grasping plant or animal plankton food. There are five basic sockets with fifteen other calcareous figures surrounding the pharynx. The plates are connected by muscles. Creatures use their Aristotle's lantern, or mouths, to scrape algae off rocks and other surfaces, as well as biting and chewing prey.

The mouth apparatus is capable of retracting into the urchin's body, as well as moving from side to side. During feeding, the five jaws are pushed out so that the mouth opens. When the urchin wants to bite, the jaws come together to grip the prey or algae and then can tear or chew by moving their mouth from side to side.

The top part of the structure is where new tooth material is formed. In fact, it grows at the rate of 1 to 2 millimeters per week. At the bottom end of the structure, there is a hard point called the distal tooth. Although this point is rigid, it has a weak outer layer that allows it to sharpen itself while it is scraping.

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GENETICS

GENETICS

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Alleles

Wild-type Alleles

Normal or Prevalent alleles in a population are called wild-type alleles. These alleles typically encode proteins that are made in the right amount and function normally.

Mutant Alleles

Dominant Alleles

A dominant allele masks or hides expression of a recessive allele and it is represented by an uppercase letter.

Recessive Alleles

A recessive allele is an allele that exerts its effect only in the homozygous state and in heterozygous condition its expression is masked by a dominant allele. It is represented by a lowercase letter. -------------------------------------------------------------

Star fish, Asterias: A Type study (P-1)

Aristotle Lantern in Echinoderms

Table of Content
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👉DNA: A Genetic Material

👉Griffith's Experiment

👉Hershey-Chase experiment

Normal or Prevalent alleles in a population are called wild-type alleles.

These alleles typically encode proteins that are made in the right amount and function normally.

A recessive allele is an allele that exerts its effect only in the homozygous state and in heterozygous condition its expression is masked by a dominant allele. It is represented by a lowercase letter.

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