# Cell Growth And Development

## Cell division

Cell division is the process by which growth repair and reproduction occur in living. Organism cell division is also responsible for distributing genetic material among daughter cell. These are two types of cell division.
(1) Mitosis
(2) meiosis

## Mitosis

It is the process of nuclear division which ensure that daughter nuclei receive some number of chromosomes as parent nuclei. It is followed by cytokinesis, a process by which cytoplasm is divided into 2 packages and hence two daughter cells are formed which have same genetic information as parent phase
Mitosis is divided into following phases :
(1) Prophase
(2) Metaphase
(3) Anaphase
(4) Telophase

Stages of Mitosis
Prophase :
Chromatin gets condensed to form chromosome which of two sister chromosomes
Mitotic spindle begin to form Nuclear envelop dissembles

Prometaphase
At the beginning of prometaphase, microtubules of the spindles attach with the kinetochores of the condensed chromosomes. Eventually, each chromosome is moved into position along a plane at the centre of the spindle
Metaphase :
Spindle fillers attaches to the kinetochore of the chromosome on both sides. Alignment of all the chromosome at the equator of the spindle (Metaphase plate)
Anaphase :
Centromere split, and sister chromatids separate from each other and move towards opposite pole.
Telophase :
The chromatids reach the opposite poles of the spindle.
Appearance of nuclear envelope endoplasmic reticulum, Golgi complex, nucleolus. Chromosome unfold to from chromatin.

Cytokinesis :
(1) In animal cell a cleavage furrow cut the cytoplasm between the two group of supported chromatics.
(2) In plant cell the cytoplasm is partitioned by the construction of new cell wall-cell plate inside the cell.
(3) at the end of mitosis two daughter cell receives identical copy of genetic material.

Significance of mitosis –
• It is responsible for development and growth of body
• It helps in repairing of tissues.

## Meiotic cell division :

It involve two successive nuclear division by which 4 haploid cells are formed by single diploid cells.

### Meiosis I

It is divided into 4 phases –
(i) Prophase I
(ii) Metaphase I
(iii) Anaphase I
(iv) Telophase I

The stages of Meiosis

Prophase I
– It is very long and complex phase which is further divided into 5 successive stages
(1) Leptotene
It is characterized by start of condensation of chromatin.
(2) Zygotene
Homologous pair of chromosomes began to pair together. The process of paring is called synapses called bivalent and tetrad.
(3) Pachytene
Crossing over between homologous chromosome occur between non-sister chromatid which is responsible for generating genetic diversity among gametes.
(4) Deponent
Mitotic spindle is assembled, and chromosome condense to their maximum compacted state. Disappearance of nuclear membrane and nucleolus occur.

Metaphase – I
The bivalent attach to spindle microtubules by their kinetochores.
Chromosomes line up on the metaphase plate.
The spindle fibers from a given pole are connected to both chromatids of a single chromosome.

Anaphase I :
homologous chromosome of each bivalent gets separated and move to opposite poles.

Telophase I and Cytogenesis
The movement of homologies chromose to opposite pole is complete. Two nuclear envelops form about one chromose each homologous pair the cytoplasm split to produce two daughter cells.

### Meiosis II :

It follows first (I) meiotic division immediately and is similar to mitosis
Interphase is very short or non-christen.
At the result of II meiotic division 4 haploid cells are form.

## Cell Cycle

The events that occur from competition of one division until the beginning of next division constitute cell cycle.
The cell cycle is divided into two parts :
Mitosis and interphase.
Interphase :
It is characterized by three phases G, phase, S-phase, G2 phase.
(i) During G Phase (Gap-1) the cell is metabolically active and grows continuously but its DNA do not replicate during this phase. Late in G, phase all cell follow one of the two paths. They may either become committed to start DNA synthesis and completed the cell cycle and withdraw from cell cycle to enter a resting phase is e Go phase. Cell that enter Go remain visible and metabolically active and does not undergo cell division. Cells under Go phase may remain undividing for rest of their life and never inter cell cycle again but at some time they may enter G phase to re-enter cell cycle. Cancer all never enter Go phase.
(ii) During S-phase replication of DNA occur.
(iii) In G2 phase (Gap-2) cell growth continues, so that cell may be prepared for mitosis.

Cell Cycle

## Cell cycle regulation

The cells ensure that the events that occur during various phases of cell cycle occur in the correct order and are coordinated. This coordination between various phases of cell cycle is dependent on the cell cycle checkpoint.
First Checkpoint (G1 /S checkpoint)
Here the cell size is monitored, if it proper and DNA has not been damaged then the cell will enter S phase.
Second Checkpoint ( G2/ncheckpoint)
If the DNA replication is not complete or any damage to DNA has not repaired cell cycle is arrested to that point.
Phase check phase :
If the spindle fibers are not found properly and their attachment to kinetochore is not proper mitosis is arrested.
Failure of any of these checkpoint controls results in genetic damage.
Molecular events at cell cycle checkpoint
Checkpoints are regulated by number of heterodimeric protein kinases.
These protein kinases have two subunits –
(1) Cyclin – It is a regulatory subunit.
(2) Cyclin dependent kinase – catalytic dependent subunit
Each CDK catalytic subunit can associate with different cyclins and associated cyclin determines which proteins are phosphorylated by the Cdk-cyclin complex. For eg – progression through G, and S is regulated mainly by cdk2, cdk4, cdk6 in association with cyclin d and e
cdk1 and cyclin A regulate profusion from S to G2, cdk1 and cyclin B regulate progression from G2 to M.

If DNA damage occur in interphase, then DNA damage checkpoint allow the repair of DNA before cell cycle resumes which is regulated by cdk1 and cdk2.

## Cell communication

All cells communicate with each other and environment. Eukaryotic cell can sense presence of molecules and response to them allowing cell-cell communication. Cell communication is accomplished by signaling molecule secreted by one cell and bind to receptor secreted by another cell.
Some common signaling molecules are nitric oxide, hormones, growth factors, cytokines etc.
Most signaling molecules bind to receptor expressed on the surface of target cells, Ether can enter the cell and bind to intracellular receptor. A large family of cell surface receptor act via guanine nucleotide binding protein these are called G-protein couple receptor. Another receptor act via phosphorylating their substrate protein at tyrosine residue.

Mechanism :
Once a signaling molecule binds a receptor O in a cell, it initiate a series of intracellular reactions towards interior of the cell and signal in transmitted from cell membrane to nucleus. Process is called intracellular signal transition.
The signal may be transmitted or involving many proteins, which is called signal transition pathway.
The molecules involved are cyclic AMP, Ca2+, calcium binding protein, calmurluliw, Mapkinase, nuclear factor-kappalian. This signaling pathway is responsible for changes in gene expression, differentiation, Replication etc A single cell may have several types of receptor each binding to specific signaling molecule.

## Movements

The various types movement are amoeboid movement.
Amoeboid movement
In this type of movement, the cytoplasm flows into the newly formed arm-like extension pseudopodia of the cell. This gradually extends and enlarges so entire cell occupies the spaces. As the cell moves new pseudopodia are moved and formed in the direction of movement and earlier ones are withdrawn.
Movement :
Cilia and flagella are thread like appendages and have similar internal structure. The difference between them relates to their different beating pattern. A flagellum beats with a symmetrical undulation that is propagated as a wave along its length. While a cilia beats with symmetrical with a fast stroke in one direction followed by slower recovery motion.
Number of flagella are very few while cilia are found in several thousands in number distributed on the surface.
Muscular Movement :
Muscle is a tissue which plays a wading role in locomotion or movement of animals.
Each muscle consist of number of muscle fibers which consist of many myofibrils, Myofibrils consist of structure called sarcomeres that do the work of contraction. Each sarcomere is bounded on two sides by dark lines called disc.
Each sarcomere consist of special protein i.e. actin and myosin.
Between actin filament lie myosin filament each of which consist of myosin molecules. In the present of energy molecules (ATP), actin filaments pull the two Z-disc inwards. In this process myosin filament slide over the actin filament that causes contraction of muscles. To exert this force, muscles are anchored to mechanical structure i.e. skeletal system contraction of muscle myosin molecule slide over actin.

Contraction of muscle during which myosin molecule slide over the actin filaments

## Nutrition

It is the process of intake of nutrients from the environment for getting energy and to maintain various body processes such as metabolic machinery, growth and developments elements of nutrition :
(1) C, H, O needed for synthesis of organic molecules like carbohydrates, fats, protein, nucleic acid.
(2) N.P.S. for synthesis of amino acid, nucleotides and lipids.
(3) Na, Ca, Mg, Cl, they exist as ion or in association with organic molecules and play some very essential role in plant growth.
(4) Mg, Cu, Zn, Co, Se and F also called force elements because needed in small amounts.
(5) Some face elements are part of vitamins and play essential function in animal nutrition

### Plant Nutrition

• Using sunlight energy and $CO_2$ atmosphere, plant synthesizes sugar molecule by photosynthesis which can be further converted into proteins and lipids.
• Most photosynthesis takes place in palliated parenchyma of leaves that lies mostly in the sunlight, upper half of the leaves.
• Spongy parenchyma specialized for CO2 lies in lower half of the leaves.
• Plants take up inorganic nutrients along with water from soil through root hairs which provide increased surface are for efficient ale sorption of water and mineral (ascent of sap).

### Animal Nutrition :

Animals cannot synthesize their own food, so they consume organic molecules synthesized by plants which is digestive or broken down to simple nutrients in the digestive tract of animals and absolved by intestine into the cells of animals, then used to obtain energy.

Vitamins :
Bacteria in the human gut synthesizes vitamin K and vitamin B12 that are absorbed by human body and utilized for various function. Human requires two types of vitamin in only small amount.
(1) Water soluble – ($B_1,\ B_2,\ B_6,B_{12},C$) folic acid, niacin’s
(2) Fat soluble – (A, E and D)
Deficiency symptoms / Disease :
(1) Deficiency of protein cause stunted growth in children.
(2) Deficiency of iron or folic acid causes anemia.
(3) Deficiency of Vitamin C cause scurvy.
(4) Deficiency of Vitamin D cause bone deformities.
(5) Deficiency of Vitamin A cause Night Blandness.
(6) Deficiency of Vitamin $B_6$ and $B_{12}$ cause nervous tissue problem.

### Saprotrophic Nutrition :

It is process in which organism feed on dead and decaying organic matter by converting complex organic molecule of plant and animals into simple nutrients is called saprophytic nutrition. These organisms are called saprophytes. Eg – microbes such as bacteria and fungus.

## Gaseous exchange

All living organisms exchange $CO_2$ and $O_2$ with their environment. Both plants and animals use oxygen for respiration and gives out $CO_2$. This exchange of gases basically involve diffusion.

Gas exchange surfaces-
(1) Cell membrane – single cell organisms like bacteria and protozoa.
(2) Earthworm and algae – through outer layer of their cell. Amphibians through skin.
(3) Gills – For example in fishes, gills have converted outgrowths containing blood vessels and covered by thin epithelia layers.
(4) Alveoli – Terrestrial animals breathe through lungs which contain millions of tiny thin walled alveoli. Alveoli provide enormous surface area and are richly supplied with blood vessels.
(5) Stomata – In plants air enters into spongy parenchyma of leaves through stomata.

## Internal transport

Nutrients taken by plants and animals are transported to various sites in the body through various sites in the body through various methods.
Circulatory system in animals –
The heart circulate bold to all parts of the body through blood vessels.
There are 3 kinds of blood vessels in human body arteries –
1) Thick walled – Carry oxygenated blood to different parts of body except pulmonary artsy.
2) Veins – Thin walled, collect deoxygenated blood from different part of body to deliver it to heart except pulmonary vein.
3) Capillaries – Very thin, narrow, connect arteries to vein to form closed circulatory system capillaries allow exchange of metabolites, nutrients and oxygen from blood into the tissues. In turn waste from tissue diffuses into the blood.

Vascular bundles in plant –
Internal transport in plants is carried by xylem and phloem.
Xylem – Xylem carries sap from the roots to the leaves. Water is pulled up by xylem through force of transpiration.
Phloem – Phloem tissue transport sap containing dissolved products of photosynthesis the phloem sap moves by asthmatically generated pressure this is called translocation.

Mechanism of translocation :
Companion cell of phloem actively pump sugar into plaloem cell (silve tubes) this causes water from surrounding leaf tissues to diffuse into sugar rich phloem cell which creates osmotic pressure in phloem cell. The non-photosynthesizing parts of plant extract sugar from the phloem for use. As sugar goes out of phloem cells water also diffuses out in the surrounding cell which lead to decrease in osmotic pressure in phloem. This difference in osmotic pressure between photosynthetic and non-photosynthetic part of plant help in mobilizing of food which is an active process.

## Reproduction

It refers to the ability of living organism to produce individual of the same species.
It involves transmission of genetic material from parental to next gen.
Reproduction ensures continuity of species.

### Reproduction in bacteria (Microbe)

Asexual reproduction
A single bacterium at successive division produce 2, 4, 16, 8 ……. and so on bacteria that is exponential or log rhythmic growth.
No genetic variation occurs hence the entire progeny is morphologically and genetically similar to parental cell.
Genetic recombination :
It is a primitive form of sexual reproduction. In this only exchange of genetic material takes place without formation of genets.
Types of genetic recombination :
1) Transformation :
The donor and recipient cell do not come in contact. A short piece of DNA is released by the donor and is actively taken up by recipient.
2) Conjugation :
It involves DNA transfer b/w cells in direct contact. The donor carries a small circular piece of DNA called F factor (fertility factor) which is responsible for formation of sex piles causing cell to all contact. Now one strand of F-factor pauses through sex piles from donor (Ft) to recipients (F-).
3) Transduction :
When any phage infect the bacterium, the DNA of the Phage gets integrated into the DNA of the bacterium and phage DNA replicate along with the bacterial DNA. Sometimes the DNA of the phage that come out of the bacterial DNA in the form of nature phage, a small piece of bacterial DNA also comes along. When such page infects a new bacteria the DNA of the previous bacteria transfers to the new recipient.

### Reproduction in plant

Asexual
New plants are produced from somatic cells or from unfertilized gametes.
Vegetative propagation :
(1) Vegetative propagation takes place when new individuals are produced from somatic cells (i.e. vegetative propagates like stem cutting, tubers. bulbils, leaves, roots etc) this does not involve seed formation.
The clone or all the individuals derived from a single cell will be exactly similar to the parent cell and each other in the terms of genotype and phenotype, and therefore such propagation is also called donor propagation.
Asexual reproduction occurs naturally (eg propagation through bulbils, leaves, roots etc) or it can be done artificially. (through stem cutting, root cuttings etc.)
(2) Apomixes :
It is a part of asexual reproduction in which embryo or seeds are developed after fertilization.

Sexual reproduction in flowering –
It occurs by the fusion of male and female gamete. Flower bear the sex organs i.e. stamen (male), pistil (female)

Male gametogenesis –
Stamen composed of filament and another. The another consist of four microsporangia. Cells of microsporangium (diploid) undergo meiosis to form microspores (haploid) which developed into pollen grains. In each pollen grain, the nucleus divide by mitosis to form two cell i.e.
(a) Vegetative Cells (tube cells)
(b) Generative cells.

Female gametogenesis
Carpel (Pistil) consists of stigma, style and ovary. Ovary contains one or more overly which is surrounded by two engagements. Only one cells of mega sporangium undergoes meiosis to from one functional megaspore (haploid). It undergo mitotic division. To form celled of nucleated embryos. One of these cells is egg cell (haploid), a central cell (2n) containing two polar nuclei

Fertilisation :
After pollination, the pollen grain stick on the stigma through germ pore, the pollen tube grows towards the ovule and enters the embryo sac releases two male gamete. One male gamete fuse with egg to form zygote (2n). The other male gamete fuses with central cell to form primary endosperm nucleus (3n). This is triple fusion. Because of syngamy and triple fusion, fertilization in angiosperm is called double fertilization.

Seed formation and germination –
Zygote undergoes mitosis and form embryo PEN provides nourishment to the developing embryo. Both embryo and endosperm are formed within ovule which gets converted into seed.
During seed germination embryo give rise to new plant by the development of plumule and radical.

Internal structure of an ovule

The pollen tube growing through stigma and style.

### Sexual reproduction in animals

(i) formation of haploid gamete which carry a single set of chromosomes derived from meiosis.
(ii) Fusion of male and female gamete which is called fertilization, result in the formation of zygote containing genetic material of both the parent.
(iii) Zygote grows and develops into mature organism of next generation.

Human Reproduction :

Male Reproductive system
Male Reproductive system is composed of a pair of testis, genital duct and accessory gland. Testis contain somniferous tubule which contain spermatogonial cell (2n). spermatogonial cell form sperm (n) through spermatogenesis.
Sperms produced in testis are carried to epididymis and then via the vas deference

Female Reproductive system :
Female reproductive system consist of ovary, fallopian Tube, Vagina, uterus and cervix. Ovaries contain oogonial cell which produce female gamete or ova by oogenesis.
Fallopian tube conveys female gamete from the ovary to the uterus. The cower entrance to the uterus is the cervix which separates the uterus from vagina.
Ovulation is the process by which mature ovum is released from the ovary to fallopian tube.
It occurs in the fallopian tube.
It Occurs in the fallopian tube. Once the sperm had entered in a acolyte, entry of other sperms is prevented. Fusion of male and female gamete is called fertilization as a result zygote is formed which give rise to new organism.

## In vitro fertilization (IVF)

In this process fertilization of gametes is done outside the body of the female that is in the test tube or Petridis in a simulated lab condition.
Fertilized ovum or zygote is then implanted into womb of the female and is allowed to develop to full term as the fertilization is carried out in a test tube or petri dishes these babies are called test tube babies.
Significance of IVF :
IVF is carried out to help infertile couples who are unable to war children normally due to medical problems. IVF is part of larger disciple called ART (Assisted reproductive technology which help couples to war babies)

## Animal development

Zygote divides into many cell, hollow sphere called blastula. Now there development of B germ layers occur normally –
(1) Endoderm
(2) Mesoderm
(3) Ectoderm
The endoderm give rise to epithelial lining of the blood, mesoderm give rise to muscle and skeletal system and ectoderm give rise to nerves and outer covering of animals the rearrangement of animals occur diving the stage gastrulation
After gastrulation, various organ develop rapidly Eg-just 3 week after development start, human have heart by the eight week head is clearly identifiable and by 121th week fingers and toes are clearly identifiable.

## Plant development :

Zygote develops into a mass of cell by mitotic division.
Two important events take place within the developing embryo.
(1) 3 layers of cells are formed from the embryo.
(2) Protoderm (it develops from outer layer of the embryo cells and give rise to outer covering of plants)
(3) Ground meristem – It gives rise to photosynthetic tissues in leaves and non-photosynthetic tissue b/w Xylem and phloem in stem and root.
(4) Procambium- It develops from inner cell of the embryo just like ground meristem give rise to xylem and phloem.
(5) The second event during development is restriction of cell division to apical meristem that lie at the two tips of embryo. One apical meristem gives rise to root system and other forms shoot system including stem, leaf and reproductive structures.

## Immune response in humans and animal

Immune system is a well-developed and efficient system to protect the human beings and animals against the attack causing organism. The protective response of the body is called immune response.

### Immune response in humans

It consist of specialized organ called lymphoid organs and the cell.
Lymphoid organs are of two types.
(1) Primary lymphoid organ Example bone marrow and thymus.
Here lymphocytes originate and then mature.

(2) Secondary lymphoid organ-lymphocyte after maturation migrate to these organs where they settle down and carry out their function.
Eg-spleen, lymph nodes and gut the cells of immune system are
(a) Lymphocytes
(b) Macrophages
(c) Natural killer all
(d) dendritic cells (DC)

### Immune response

When a pathogen enters a human body through skin or other body surfaces, the lymph carries it to lymph nodes.
Lymph nodes have B-lymphocytes, T-lymphocytes and Macrophages.
Macrophages engulf the pathogen and break it down by the enzymes.
Now macrophages present components of pathogen to T-lymphocytes. Several cellular mechanisms occur, and interleukins are produced. Under the influence of interleukins B-lymphocytes and T-lymphocytes gets activated. After activation B-lymphocytes produce antibodies which react with pathogen and destroy it. There are 5 different classes of antibodies (immunoglobulins) named as IgG, IgM, IgE, IgD, IgA.
Antibodies are glycoproteins present in plasma each contain 4 polypeptide chain two heavy and 2 light chain together.
The type of immune response which is mediated by antibodies is called humoral response.

Diagrammatic structure of an immunoglobulin (Ig) molecule

Interleukins also activates T-lymphocytes, macrophages and natural killer cell. These activated cells attack those cells of the host which harbor pathogen and kill them this called cell mediated immunity.
Question
What are photolytic cell? Write their functions.
Any of various specialized cells that engulf or ingest other cells or particles. In vertebrate’s animal phagocytosis are WBC’s that break down bacteria note : and other microorganism, foreign particle etc.
These include monocyte, macrophages and most granulocytes.

## Program cell therapy :

It is basically a cell suicide. Cells undergoing PCD shows distinctive morphological features which are collectively called apoptosis. PCD is a highly order passage in which cells are disassembled very systematically. The cells detaches from neighboring cell. Cytoplasm and nucleus condenses, and mitochondria lose their membrane integrity and their content leak into cytoplasm.
By the condensation of chromatin, its breakdown into smaller fragments by the action of enzyme endonucleases. Finally, the cell membrane starts to form bloods and cell gets fragmented in apoptotic bodies which are engulfed by macrophages.
The development of finger and toes in the developing fetus occur by the apoptosis.
Note : Mecrosts
It is a form of chromatid cell death that results from acute cellular injury. In this the injured cells swell and fall apart releasing their content.

## Defense mechanism in plants :

Plants possess defense mechanism to fight the pest and pathogen. Plant defense system can be classified as either passive (constitutive) or active (inducible depending upon wither they are pre-existing in plant or are switched on after infection.

Passive defense
The presence of cuticle bark and sign in prevents penetration of microbes into the plant cell. Plant synthesizes secondary metabolites such as phenols. Labroids, linins etc. which are toxic pest and pathogens.

Active defense
After the invasion of the pathogen the cell wall becomes thick which impedes penetration of pathogen. These are called wall apposition Hypersensitive response is observed in which the host cell surrounding the site of infection gets necrotic. These cells also show changes in oxidative metabolism and accumulation of toxic compound. The overall effect is highly unfavorable which restrict the spread of pathogen.
In response to infection plant cells produce phytoalexins with inhibitory action against microorganism.

Question
What are phytoalexins Write their role in defense system?
Phytoalexins are small molecular weight compounds that are produced by plant cell in response to the infection. These are synthesized in plant tissue and accumulate in response to microbial challenges or other type of stress.
When synthesis of phytoalexins is inhibited using certain inhibitors, the resistance to pathogens decreases.

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