Differentiate between Prokaryotic and Eukaryotic cells

SECTION - III

Attempt any THREE questions:                                                                        (8 x 3 = 24)

Q.6 

       (a) Differentiate between Prokaryotic and Eukaryotic cells.

Ans.        PROKARYOTIC AND EUKARYOTIC CELLS:

Biologists have divided cells into two types: prokaryotic and eukaryotic.
The differences between these two types of cells are mainly based upon the structure of their nuclei.

Eukaryote

Prokaryote

(i) Eukaryotes have a very well defined nucleus, in which nuclear material (chromosomes or DNA) is enclosed in a double nuclear membrane. (ii) Those possessing eukaryotic cells are called eukaryotes. (iii) Eukaryotes includes all other unicellular or multicellular organisms such as animals, plants, fungi and protista. (Containing all membrane bounded organelles) (iv) Ribosomes compared of eukaryotes 80S. (v) The cell wall of plants is generally made up of cellulose. (vi) Eukaryotic cells are given in diagram.

(i) In prokaryotic cells, however the genetic material (DNA) is without any nuclear membrane covering and is directly submerged in the cytoplasm. (ii) Organisms possessing prokaryotic cells are called prokaryotes. (iii) Prokaryotes include bacterial and blue green algae. Prokaryotic cells generally lack many of the membrane bounded structures found in eukaryotic cells, For Example, mitochondria, endoplasmic reticulum, chloroplast and Golgi apparatus are absent in prokaryotic cells. Since there is no nuclear membrane, a prokaryotic cell has no distinct nucleus and its DNA molecule is directly suspend in cytoplasm. (iv) Prokaryotes have small sized ribosomes 70S. In prokaryotes mitosis is missing and the cell divides by binary fission. Because of their simpler structure, it was widely accepted for a long time that prokaryotic cells represent a more primitive stage of evolution than eukaryotic cells Perhaps the most distinctive features of the prokaryotic cell is its cell wall, composed of polysaccharide chains bound covalently to shorter chains of amino acids forming. Peptidoglycan and Murein. (v) The entire cell wall is often regarded as a single huge molecule or molecular complex called Sacculus or murein and is differently structured than that of a bacterium. (vi) Diagrams of prokaryotic.

Q.6 

        (b) Explain the nutrition in fungi.

Ans.     NUTRITION IN FUNGI:

• All fungi lack chlorophyll and are heterotrophs (obtaining carbon and energy from organic matter).
• They obtain their food by direct absorption from the intermediate environment and are thus absorptive heterotrophs.

(1) Saprotrophs:

• Most fungi are saprotrophs (or saprobes), decomposers that obtain their food (energy, carbon and nitrogen) directly from dead organic matter.
• They secrete out digestive enzyme which digest dead organic matter, and all organic molecules thus produced are absorbed back into the fungus.
• Saprobic Fungi anchor to the substrate by modified hyphae, the rhizoids.
• Fungi are the principal decomposers of cellulose and lignin, the main components of plant cell walls (most bacterial cannot break them).
• Extensive system of fast growing hyphae provides enormous surface for absorptive mode of nutrition.
• Saprobic fungi, along with bacteria, are the major decomposers of the biosphere, contributing to the recycling of the elements (C, N, P, O, H etc) used by living things.

(2) Parasites:

Some fungi are parasites.

Haustoria:

• Parasitic fungi absorb nutrient directly from the living host cytoplasm with the help of special hyphal tips called hustoria.
• They may be obligate or facultative.

(i) Obligate Parasites:

• Obligate parasites can grow only on their living hosts and cannot be grown on available defined growth cultures medium.
• Various mildews and most rust species are obligate parasites.

(ii) Facultative Parasites:

• Facultative parasites can grow parasitically on their host as well as by themselves on artificial growth media.

(3) Predators:

Some fungi are active predators.

(i) Oyster Mushroom (Pleurotus Ostreatus) is a carnivorous (predatory) fungus:

• It paralyses the nematodes (that feed on this fungus), penetrate them, and absorb their nutritional-contents, primarily to fulfil its nitrogen requirements.
• It fulfills its glucose requirements by breaking the wood.

(ii) Arthrobotrys:

Some species of arthrobotrys trap soil nematodes by forming contricting ring, their hyphae invading and digesting the unlucky victim. Other predators have other adaptations, such as secretion of sticky substances.

(4) Mutualistic Symbiotic:

• Fungi form two key mutualistic symbiotic association (associations of benefit to both partners).
• They are lichens and mycorrhizae.

(i) Lichens:

• Lichens are mutualistic and have symbiotic associations between certain fungi mostly Ascomycetes and imperfect fungi, and few Basidiomycetes (about 20 out 15000 species of lichens) and certain photoautotrophes either green algae or a cyanobacterium, or some times both.
• Most of the visible part of lichens consist of fungus and algal components are present within the hyphae.
• Fungus protects the algal partner from strong light and desiccation and itself gets food through they courtesy of alga.
• Lichens can grow at such place where neither of the components along can even at harsh places such as bare rocks etc.
• Lichens vary in colour, shape, overall appearance, growth form.

Bioindicators: They are ecologically very important as bioindicators of air pollution.

(ii) Mycorrhizae:

• Mycorrhizae are mutualistic association between certain fungi and roots of vascular plants (about 97% of all kinds of vascular plants).
• The fungal hyphae dramatically increase amount of soil contact and total surface area for absorption and help in the direct absorption of phosphorus, zinc, copper and other nutrients from the soil into the roots. Such plants show better growth than those without this association.
• The plant, on the other hand, supplies organic carbon to fungal hypahe.

Types:

There are two main types of mycorrhizae

(a) Endomycorrhizae:

Endomycorrhizae, in which the fungal hyphae penetrate the outer cells of the plant root, forming coils, swellings and minute branches, and also extend out into surrounding soil;

(b) Ectomycorrhizae:

Ectomycorrhizae in which the hyphae surround and extend between the cells but do not penetrate the cell walls of the roots. These are mostly formed with pines, firs etc.

However, the mycelium extend far out into the soil in both kinds of mycorrhizae.

Habitat:

Fungi grow best in moist habitats, but are found wherever organic matter is present.

Temperature and pH:

• They survive in dry conditions in some resting stage or by producing resistant spores.
• They can also tolerate a wide range of pH from 2 - 9, a wide temperature range, and high osmotic pressure such as in concentrated salt/sugar solutions as in jelly, jam etc.
• These features also help them in their survival on land.

Reserve food Material:

Fungi store surplus food usually as lipid droplets or glycogen in the mycelium.