(a) Lamarck’s theory of the inheritance of acquired characters: Lamarck’s theory was based on the following four points:

(1) All organisms tend to increase in size to a predetermined limit.

(2) New organs are produced due to a new need.

(3) Development or degeneration of organs is due to constant use or disuse of them.

(4) The modifications acquired by an organ of an individual in one generation are transmitted to the next generation.

(b) Darwin’s theory of Natural selection: Darwin published his view of evolution in a book called the “Origin of Species”. His contemporary Russell Wallace also had independently the same ideas on evolution. Darwin’s theory of evolution by natural selection was based on Over production, Variation, Struggle for Existence and Natural selection

(c) The current synthetic theory of evolution recognizes the basic types of processes-Gene mutation change in chromosome number and structure, genetic recombination, natural selection and reproductive genetic variability with which change cannot take place natural selection and reproductive isolation guide populations of organisms into adaptive channels. 

(i) Cell wall: The protoplasm of plant cells is separated from the external world by the cell wall, which is entirely lacking in animals. The cell wall is secreted by the cell itself and primarily it contains a complex polysaccharide, the cellulose. 

(ii) Plasma-membrane: Most plant and animal cells have an external covering known as plasmalemma or plasma membrane. It is a living, ultra thin, elastre, porous, semi permeable membranous covering of cell. Primarily, it provides mechanical support and external form to the protoplasm. 

 

Cytoplasm

CELL-DIVISION

• The growth and the development of every organism depend exclusively on the multiplication and enlargement of its cells. The development of a multicellular organism from the unicellular zygote is achieved by the cell division, growth and differentiation.
• The division of the nucleated cells is achieved by two integral activities such as division of the nucleus (called Karyokinesis) and the division of the cytoplasm (that is called cytokinesis). Usually the Karyokinesis is followed by cytokinesis, but sometimes is does not follow and results in multinucleated cells.
• In animals and plants following three types of cell division have been observed:
• 1. Amitosis 2. Mitosis 3. Meiosis

Amitosis

• It is the means of asexual reproduction in unicellular organisms like bacteria and protozoan. It also occurs in embryonic membranes of vertebrates. In Amitosis, the splitting of nucleus is followed by cytoplasmic constriction. In Amitosis, two daughter cells are formed without the occurrence of any nuclear event. It is also known as direct nuclear division.

• The process of Mitosis was first observed in animal cells by W.Flemming (1882) in Salamandar (Tritus maculosa) and in plant cells by Strasburger. An organism’s body has two kinds of cells, the somatic cells and germ cells. Germ cells occur only in the gonads and are concerned with reproduction whereas Somatic cells in the remaining bulk of the body. Mitosis occurs in the somatic cells whereas meiosis occurs in germ cells.
• A cell, from the time it makes its appearance as a daughter cell to the time when it starts dividing is called an Interphase cell or Resting phase. An interphase cell has a pair of centrioles and a prominent nucleus with nuclear membrane and nucleolus. The chromatic threads are very thin and long and form a network, called the chromatin reticulum. In interphase stage only DNA replication occurs.
• The process of mitosis can be distinguished into 4 stages. 
  (1) Prophase 
  (2) Metaphase 
  (3) Anaphase 
  (4) Telophase. 

• There is no sharp line of demarcation between the successive phases. Prophase is the longest phase of mitosis. It involves a number of changes in the cell. First of all the two sets of paired centrioles move apart and migrate towards the opposite poles of a cell. Side by side, the five-chromatin threads shorten and thicken by spiral coiling. These threads are now known as chromosomes. The chromosomes further shorten and thicken and each splits into two identical chromatids. The two chromatids remain attached to the centromere and each possesses a complete set of DNA molecule. Simultaneously, the nucleolus and nuclear membrane gradually disappear and the nuclear material mixes with the cytoplasm. With these changes, the prophase comes to an end. In metaphase, the chromosomes with their chromatins still attached, move towards the equatorial plane of the cell i.e. the plane midway between the two poles. In anaphase each centromere divides to separate the two sister chromatids. The sister chromatids, now called chromosomes, repel each other and migrate towards the opposite poles. After the arrival of the chromosomes at the poles the spindle fibers disappear. This is followed by Telephase which may be called as reconstruction or reorganization phase. At this stage the chromosomes uncoil, become thinner and longer and finally form the chromatin. A nuclear membrane reappears around each set of chromosomes leaving the centroles outside it. A nucleolus appears in each daughter nucleus. The division of the nucleus i.e. Karyokinesis, is followed by division of the cytoplasm i.e. cytokinesis. It begins as a constriction or cleavage furrow that appears in the cytoplasm in the equatorial region during the late anaphase. The furrow gradually deepens and finally divides the cell into two daughter cells.

Meiosis / Reductional Division
Term Meiosis was given by Farmer and Moore in 1905. Meiosis occurs in the cells of gonads (testis and ovaries), resulting in the formation of gametes (sperms and ova). Unlike mitosis, meiosis involves two cell divisions. The first meiotic division is the reduction division resulting in two haploid daughter cells, while the second is the equational division dividing each haploid daughter cell into two similar haploid cells. Thus four haploid daughter cells are produced by a diploid parent cell.
Meiosis results in the formation of haploid sex cells, which after fertilization restore the original diploid number in the zygote It is thus responsible for maintaining the fixed number of chromosomes in a species.
The phenomenon of crossing over provides new comlanation of chromosomes and hence new combinations of characters in offspring.

Meiosis / Reductional Division

• Term Meiosis was given by Farmer and Moore in 1905. Meiosis occurs in the cells of gonads (testis and ovaries), resulting in the formation of gametes (sperms and ova). Unlike mitosis, meiosis involves two cell divisions. The first meiotic division is the reduction division resulting in two haploid daughter cells, while the second is the equational division dividing each haploid daughter cell into two similar haploid cells. Thus four haploid daughter cells are produced by a diploid parent cell.
• Meiosis results in the formation of haploid sex cells, which after fertilization restore the original diploid number in the zygote It is thus responsible for maintaining the fixed number of chromosomes in a species.
• The phenomenon of crossing over provides new comlanation of chromosomes and hence new combinations of characters in offspring.

ANIMALS TISSUES

• Four types of tissues have been identified in the animal kingdom, they are: Epithelial tissues, Connective tissues, Muscular tissues, Nervous tissues

Epithelial Tissues 

• This tissue covers, organs both externally and internally. Cells are closely placed together without any intercellular spaces. The shape and size of the cells constituting epithelial vary from organ to organ. Epithelial tissues are of two kinds:
  (a) Simple epithelial tissues: Cells are arranged to form single layer. 
  (b) Compound epithelium tissue: These epithelia are made of more than one layer. 

Connective Tissue

•  It connects one tissue or organ with other tissues/organ, hence called connective tissue. The cells are found scattered in the ground substance and the matrix is an inert fluid. By and large, three kinds of connective tissues have been recognized:Connective tissue proper, Skeleton tissue, Fluid connective tissue

Cartilage

• It is relatively soft, flexible supporting tissue. It has dense matrix with cartilage cells, chondrocytes, scattered in the matrix. Smaller chondrocytes are more numerous found near the margin and larger but few cells in the centre, cells are found individually or in groups of two or four and are surrounded by smooth and clear wall called lacunae. Surface of cartilage is formed by tough connective tissue fiber called perichondrium. There are no blood vessels hence nutrition is simply by diffusion. It is of three types: (i) Hyaline (ii) Elastic, (iii) Fibrous

Bone

• Bones are relatively harder than cartilage because the matrix consists of elastin fibers, which are saturated with phosphates and carbonates of calcium and magnesium. Bones of the whole body articulate to form skeleton that provide definite shape to the body. Almost all long bones of the vertebrate bodies are hollow. Around this cavity are osteocytes that are the bone cells in concentric rings. The outer surface is composed of dead lamellae enclosed by periosteum. The osteocytes are embedded in the matrix. Short filamentous structures arise from every osteocyte and with which all osteocytes are inter connected with each other. These are called canaliculi. The central cavity is filled with bone marrow, which is of two types:
  (i) Red marrow: which produce Red Blood Cells (RBC).
  (ii) Yellow marrow: primarily stores fat but sometimes produces RBC also.
•  Haversian canals: These are characteristics feature of mammalian bones which is system of branched tubular structures that traverse through the thick solid portion of the bones and supply nourishment to the bones. One Harvesian canal is connected to another by horizontal canal called as Volk’s man canal.

Fluid connective tissue

• This is found in fluid state and circulates through the body. There are two types of fluid connective tissue, that is:
•  (i) Blood (ii) Lymph
•  (i) Blood: Blood performs several vital functions of the body. It distributes nutrients, oxygen etc. and maintains a uniform body temperature. It is made up of fluid matrix called plasma and several types of cells termed formed elements. The plasma form 54% of the blood volume and the cells 45%. The formed elements consist of red blood cells (RBC) or erythrocytes. White Blood Cells (WBC) or leucocytes and Platelets or thromobocytes. Blood plasma is the straw-coloured fluid obtained when all formed elements are removed from blood. The ratio of plasma to formed element is held relatively constant by the homeostatic control of the body. Term homeostasis by Cannon.
•  (ii) Lymph: Lymph is an extracellular fluid drained by lymph vessels. Lymph is yellow coloured fluid when is formed by the selective absorption of the interstitial fluid in the lymphatic capillaries. Lymph constitutes about 25% of the total weight of all mammals, the lymphatics are present nearly in all parts of the body. The movement of the lymph is brought about by breathing movements and contraction and relaxation of skeletal muscles of the body. At many points in the body where the smaller lymph vessels join the larger ones, masses of cells aggregate to form lymph nodes, which produce lymphocytes and antibodies, and filter out bacteria and foreign particles. Lymph plays a major role in body’s Defence against disease by the production of lymphocytes and antibodies, and by filtering action of the lymph nodes.

FACTS ABOUT BONE
1.	Bones are made up mostly of the mineral, calcium and phosphorous. There is protein in bones too, to give them some flexibility.
2.	Only long spongy bone have spaces inside them filled with bone marrow. There is a red bone marrow found in mid of long bones. The RBCs and WBCs are produced in bone marrow.
3.	There are 206 bones in the body. The thinnest one is inside the ear names stapes
4.	The skull is made of 22 bones. The ceranium acts as a helmet to the brain
5.	The longest bone in the body is femur

Muscular Tissue

•  Muscles that are made of long muscles fibers constitute muscular tissue. It is mainly concerned with the movements of different kinds. The muscular fibers are placed tightly to form bundles. Broadly speaking there are 3 kinds of muscles in mammals:
  (i) Fast moving muscles or striated muscles (e.g. voluntary muscles striped muscles or skeletal muscles etc.)
  (ii) Slow muscles or non-straited muscles including visernal minusedes, smooth muscles, involuntary muscle etc.)
  (iii) Medium fast muscles or cardiac muscles (e.g. Heart muscles).

Nervous Tissue

•  In mammals all body activities are either directly or indirectly under the control of the nervous system. The stimuli, which the nervous system receives, are of two kinds: stimuli or sensations. Like pressure, pain, heat etc. which are caused due to changes in the external conditions, are called exteroceptive sensations. Sensations, which convey the physical state of the body, are called proprioceptive sensations. Both extero and proprioceptive sensations are brought to the brain and spinal cord through sensory nerves. Orders, which are carried out in response to these sensations, are conveyed to the appropriate organs through motor nerves. 

Facts about hair and skin
The main reason one’s hair is blond, another’s is red and still another is black that their hair contains different amount of borwn-black melanin, the colouring pigment found in the skin. The more of it in the hair the darker the hair is.
Turning white of hair means melanin is no longer being added to the new hair cells as they develop in the follicle.
Two chemicals called melanin and carotene give sin its colour. They are found in the outer of the skin the emidermis. The melanin gives the skin brown-black tones, and the carotene gives it yellowish tones. The pink tones in the colour of the skin came from all the tiny blood vessels near the surface. Melanin protects skin from Sunborn, so in very hot countries the people had lots of malanin in their skin, which make their skin dark.
The thin outer layer is called epidermis
It is made up of dead skin cells
There are no blood vescles in this layer
The skin’s colour is in this layer
It is what tans to protect light-skinned people from the sun’s burning rays.
The thicker inner layer is called ‘Dermis’ it is filled with blood vessels, nerves, hair follicles and sweat glands.
The sweat gland, take water from the blood and push it out as sweating.
Under the dermis there is a layer of fat cells, which projects one from cold and is the body’s extra fuel supply.
When one is embarrassued, blood vessels in the skin of one’s face and neck dilate (open wider) and fill with extra blood. This what is called a blushing