UPSC

Cell     Components of Cell? In the living organism there are two types of cellular organizations. If we look at very simple of cellular like bacteria and blue-green algae, we will discover cells that have no defined nucleus, these are prokaryotes cells. The cells which have definite nucleus are known as eukaryote. But the things which both have in common is that there are compartments surrounded by some type of membranes. These are called cell membranes.   Cell membranes: It is like a plastic bag with some tiny holes that bag holds all of the cell pieces foreign particles outside the cell. The holes are there to let some things move in and out of the cell. Compounds called proteins and phospholipids make the basic bag. The proteins are found around the holes and help move molecules in and out of the cell. Substances like more...

Tissue     Epithetical Tissue It is a tissue that is made up of tightly packed cells. Without much materials with in these cells. The reasons for the tightly packed cells are to act a barrier against mechanical injury, invading micro-organisms and fluid loss. We can define epithetical tissue by considering two points in mind one is the number of cells layers and two the shape of the cells. (i) On the basis of cell layers (a) When an epithelium has a single layer of cells it is called a simple epithelium. (b) Where as a multiple tier of cells are known as stratified epithelium.  (ii) On the basis of simple shape of cells:  

• Cuboidal: its occurrence is in kidney tubules, salivary glands, inner lining of the cheek. Its main function is give mechanical strength.

 

• Columnar: its more...

Muscular and Skeletal System     Skeletal Systems of Various Animals (i)   Movement is a major characteristic of animals. This movements is a result of contraction of muscles. The skeleton helps transmit that movement. Skeletons are either a fluid-filled body cavity, exoskeletons or internal skeletons.   (ii)   Hydrostatic skeletons consist of fluid-filled closed chambers. Internal pressures generated by muscles contraction cause movement as well as maintain the shape of the animals, such as the sea anemone and worms. The sea anemone has one set of longitudinal muscles in the outer layer of the body, and a layer of circular muscles in the inner layer of the body. The anemone can elongate or contract its body by contracting one or the other set of muscles.   (iii)  Exoskeletons are characteristic of the Phylum Arthropoda. Exoskeletons are hard segments that cover the muscles and visceral organs. Muscles for more...

The Nervous System     Divisions of the Nervous System

• The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops.

 

• The Central Nervous System (CNS) includes the brain and spinal cord.

 

• The Peripheral Nervous System (PNS) connects the CNS to other parts of the body, and is composed of nerves (bundles of neurons).

 

• Not all animals have highly specialized nervous systems.

 

• Those with simple systems tend to be either small and very mobile or large and immobile.

 

• Large, mobile animals have highly developed nervous systems: the evolution of nervous systems must have been an important adaptation in the evolution of body size and mobility.

  Nervous System in more...

The Endocrine System     Hormones The endocrine system is a collector of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at target organ, which has cells processing the appropriate receptor. Exocrine glands (not part of the endocrine system) secrete products that the passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands. Hormones are grouped into three classes based on their structure:

steroids

peptides

amines

 

Steroids

Steroids are lipids derived from cholesterol. Testosterone is the male sex hormone.   Estradiol, similar in structure to testosterone, is responsible for many female sex characteristics. Steroid hormones are secreted by the gonads, adrenal cortex, and placenta.  

Peptides and

Amines

Peptides are short chains of amino acids; most hormones are peptides. They are secreted by the pituitary, parathyroid, heart, more...

Lymphatic System and Immunity     The Lymphatic System

• The lymphatic system is composed of lymph vessels, lymph nodes, and organs. The functions of this system include the absorption of excess fluid and its return to the blood stream, absorption of fat (in the villi of the small intestine) and the immune system function.

 

• Lymph vessels are closely associated with the circulatory system vessels. Larger lymph vessels are similar to veins. Lymph capillaries are scatted throughout the body. Contraction of skeletal muscles causes movement of the lymph fluid through valves.

                   

• Lymph organs include the bone marrow, lymph nodes, spleen, and thymus.

 

• Bone marrow contains tissue that produces lymphocytes. B-lymphocytes (B-cells) mature in the bone marrow.

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The Respiratory System     Respiration in Single Cell Animals Single-celled organisms exchange gasses directly across their cell membrane. However, the slow diffusion rate of oxygen relative to carbon dioxide limits the size of single celled organisms. Simple animals that lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans, which are the most efficient for gas exchange. However these simple animals are rather small in size.   Respiration in multicellular animals Large animals cannot maintain gas exchange by diffusion across their outer surface. They developed a variety of respiratory surfaces that all increase the surface area for exchange, thus allowing for larger bodies. A respiratory surface is covered with thin, moist epithelial cells that allow oxygen and carbon dioxide to exchange. Those gases can only cross cell membranes when they are dissolved in water or an aqueous solution, thus respiratory surfaces must be more...

The Circulatory System     Circulatory Systems in Single-celled Organisms Single-celled organisms use their cell surface as a point of exchange with the outside environment.   Sponges are the simplest animals, yet even they have a transport system. Seawater is the medium of transport and is propelled in and out of the sponge by biliary action.   Simple animals, such as the hydra and planarian lack specialized organs such as hearts and blood vessels, instead using their skin as an exchange point for materials. This, however, limits the size an animals can attain. To become larger, they need specialized organs and organ systems.   Circulatory Systems in Multicellular Organisms Multicellular animals do not have most of their cells in contact with the external environment and so have developed circulatory systems to transport nutrients, oxygen, carbon dioxide and metabolic wastes. Components of the circulatory system include            more...

The Reproductive System     Asexual reproduction                         

• Asexual reproduction allows an organism to rapidly produce many offspring without the time and resources committed to courtship, finding a mate, and mating.

 

• Fission, budding, fragmentation, and the formation of rhizomes and stolon’s are some of the mechanisms that allow organisms to reproduce asexually.

 

• The hydra produces buds;

 

• Starfish can regenerate an entire body from a fragment of the original body.

 

• The lack of genetic variability in asexuality reproducing populations can be detrimental when environmental conditions change quickly.

  Sexual Reproduction

• In sexual reproduction new individuals are produced by the fusion of haploid gametes to more...

Plant Reproduction     Flowering plants Flowering plants, the angiosperms, were the last of the seed plant groups to evolve, appearing over 100 million years ago during the middle of the Age of Dinosaurs (late Jurassic). All flowering plants produce flowers and if they are sexually reproductive, they produce a diploid zygote and triploid endosperm.                 Flowers Flowers are collections of reproductive and sterile tissue arranged in a tight whorled array having very short internodes. Sterile parts of flowers are the sepals and petals. When these are similar in size and shape, they are termed tepals. Reproductive parts of the flower are the stamen (male, collectively termed the androecium) and carpel (often the carpel is referred to as the pistil, the female parts collectively termed the gynoecium).   Pollen Pollen grains (from the greek palynos more...