Biology Class 9 Notes- Chapter 2

Structural Organization of Life

Q No.1. Define discovery of cell and cell theory.

Ans.     In 1665, Robert Hook made a microscope by combining lenses, called compound microscope and examined a slice of cork under it. He found small honey comb like chambers which were like small rooms, so he names these structures as cellulae or cell (small rooms). The cork was made of bark of oak (Shah Baloot) so he saw cell wall only.

            In 1842, Dutrochet, boiled plant material in nitric acid and then examined under microscope, he found cells. In 1831, Robert Brown discovered nucleus in the cell of orchid. Later the combined efforts of Schleiden (1838), Theoder Schwann (1839) and Rudolf Virchow finally gave a cell theory;

            The salient features of cell theory are;

I)                   All living organisms are composed of one or more cells.

II)                The cell is the basic, structural and functional unit of all organisms.

III)             New cells are formed by the division of pre-existing cells.

Q No. 2. Differentiate between Light Microscope and Electron Microscope.

S. No.	Light Microscope	Electron Microscope
1.	It Uses visible light as a source of illumination.	It uses beam of electron as a source of illumination.
2.	Glass lenses are used for magnification.	Electromagnet is used as lenses.
3.	Light microscope can magnify the object up to 1000 times.	Electron microscope can magnify the object up to 10,000,000x times.
4.	Its resolution power is just 0.2 m.	Its resolution power is 0.2 nm, a thousand times improvement over light microscope.
5.	The image of object can be focused in human eye.	Screen or photographic plates are used to focus images.

Q No. 3. Differentiate between Resolution and Magnification.

Ans.

S. No.	Resolution	Magnification
1.	Resolution is the capacity to separate the adjacent objects.	Magnification is the mean of increasing the size of the object.
2.	It is maintained while increasing magnification.	Resolution is disturbed while increasing magnification.
3.	It improves when length of illumination becomes shorter.	It improves with the focal length of lens.

Q No. 4. How cell is the structural and functional unit of all living organisms?

Ans. Microscopic studies reveal that all living organisms are composed of cells. Therefore, it is the unit of structure of living organisms. Cells are of different sizes and shapes so they perform different functions. All basic functional activities occur in the cell. Therefore, it is also unit of function of all living organisms.

Q No. 5. Write a note on cell wall.

Ans. Cell wall is the non-living outermost boundary in plant cells. It is secreted by protoplasm of plant cell.

Ø  In plant cell it is mainly composed of cellulose and pectin. Cellulose make the fibers which are arranged in criss cross manner. These fibers are kept in position by a cementing material called calcium pectate (Pectin).

Ø  Bacterial cell-wall is made up of protein and carbohydrates.

Ø  Fungal cell-wall is made up of fungal cellulose and chitin.

Cell wall in plants is made up of three layers:

Ø  Middle lamella: Formed between the primary walls of neighboring cells.

Ø  Primary wall: Chemically composed of cellulose and pectin and sometimes lignin.

Ø  Secondary wall

Ø  Sometimes tertiary wall

Function: It provides protection, support and shape to the cell. It is a permeable in nature.

Q No. 6. Write a note on cell membrane.

Ans. Cell membrane or plasma membrane is an outer layer in all types of cells except plant and bacterial cell.

Structure: Cell membrane consists of two layer of Phospho-lipid in which protein molecule floats like iceberg. This basic structure is called Fluid Mosaic Model presented by Singer and Nicholson (1972). This basic structure is also found in membranes of mitochondria, chloroplasts etc.

Function: Cell membrane is selectively permeable membrane. In many animal cells the cell membrane infolds, taking in materials in the form of vacuole. This process is called endocytosis.

Q No. 7. Write a note on Nucleus or Karyon.

Ans. Nucleus was discovered by Robert Brown in 1831. It controls all activities of cell. It may be spherical or irregular in shape. It is usually present in center in animal cell while pushed towards cell membrane in plant cell due to a large vacuole. Nucleus is covered by double nuclear membrane which possesses large number of nuclear pores. It is filled with jell like nucleoplasm, which contains nucleolus and thread like structures the chromatin network. Each thread is called chromosome which is composed of DNA (Deoxyribo nucleic acid) and protein.

Q No. 8.  Write a note on cytoplasm.

Ans. Cytoplasm is a fluid portion lying in between cell membrane and nucleus. It consists of aqueous matrix called cytosol and cytoplasmic organells.

Composition: Cytoplasm is composed of 90% water and other solutions. Many metabolic reactions like protein synthesis, glycolysis take place in it.

Some important cytoplasmic organelles are:

1.      Endoplasmic reticulum 2. Golgi complex 3. Mitochondria 4. Plastids 5. Centrioles

6. Ribosomes 7. Vacuoles

Q No. 9. What are Endoplasmic reticulum and Golgi complex?

Ans. (Endo=Inside, plasma=protoplasm, reticulum=network). It is the network of tubules throughout the cytoplasm, which are in contact with plasma membrane and nuclear membrane. There are two types of endoplasmic reticulum:

1.      Rough Endoplasmic reticulum: Having ribosomes at outer surface and involve in protein synthesis.

2.      Smooth Endoplasmic reticulum: It maintains the shape of cell and detoxifies the harmful effects of drugs.

Golgi complex were discovered by Camillo Golgi. They are the smooth membranes stacked into fluid filled sacs containing carbohydrates. Cell secretions are done by Golgi complex.

Q No. 10. What are Mitochondria and plastids?

Ans. Mitochondria are bean shaped organelles consisting of double membrane. The infoldings in inner membrane are called cristae while fluid inside it is called matrix. Mitochondria contain enzymes which break food for the production of energy, so they are called power house of cell.

Plastids are found in cells of higher plants. They contain different types of pigments. Plastids are of three types on the basis of pigment colour:

I.                   Chloroplast: It has green pigment i.e. Chlorophyll found in leaves and green parts of plants.

II.                Chromoplast: Have coloured pigment other than green. Found in fruit, flowers, petals and other coloured parts of plants.

III.             Leucoplast: (Leucos=white or colourless) found in cells of underground parts of plants. They store food in the form of starch.

Q No. 11. Write short notes on following:

I.                   Centrosome and centrioles: A round centrosome is present is present near the nucleus in animal cell. A centrosome contains two centriols, each consists of 9 m

II.                icrotubules. They form fibrous protein spindle during cell division.

III.             Ribosome: They are ribonucleic (RNA) acid rich granules. They are attached on the surface of rough endoplasmic reticulum as well as found as free. They are sites for protein synthesis hence called protein factories of cell.

IV.             Vacuole: They are the fluid filled sacs surrounded by a membrane called tonoplast. They store cell sap. In animal cell they are numerous while in plant cell there is a large vacuole in center.

Q No.12. What are Prokaryotic and Eukaryotic cells?

Ans. a. Prokaryotic (Pro=before, Karyon=nucleus) cell does not possess true nucleus, it means its nuclear membrane is absent. These types of cells are found in bacteria and cyanobacteria (blue green algae). Such organisms are called Prokaryotic organisms.

            b. Eukaryotic (Eu=true, Karyon=nucleus) cell possess proper nucleus where nuclear material is enclosed in proper nuclear membrane. These types of cells are found in plants and animals and such type of organisms are called eukaryotic organisms.

Q No.13. Differentiate between prokaryotic and eukaryotic cells.

Ans.

Q No.14. What is cell division?

Ans. New cell after growing to maximum size: may undergo the process of cell division. During this process, the division of nucleus is called Karyokinesis (Karyon=nucleus, kinesis=division) and division of cytoplasm is called Cytokinesis. Thus two daughter cells arise from single division of cell. There are two main types of cell division 1. Mitosis 2. Meiosis.

Q No. 15. Describe Mitosis and its phases.

Ans. In Mitosis parent cell divides into two daughter cells in a way that number of chromosomes in the daughter cells remains the same as in the parent cell. Karyokinesis can be divided into four phases:

1.      Prophase: During early prophase chromosomes appear. Each chromosome consists of two chromatids. Two chromatids in a chromosome are attached to each other at centromere. Nuclear membrane disappears and centrosome divides into two centrioles, each move to the opposite pole of the cell and forms the spindle fibres. The centrioles are absent in plant cell.

2.      Metaphase: During metaphase each chromosome arranges itself on the equator of the spindle. Each chromosome is attached to separate spindle fibre by its centromere.

3.      Anaphase: During anaphase centromere of a chromosome divides and chromatids separate from each other and move towards opposite poles. In this way each chromatid is now an independent chromosome. One set of chromatid move towards one pole while other set move towards other pole.

4.      Telophase: During Telophase chromatids (now called chromosomes) reach the poles and their movement ceases. Each pole receives same number of chromosomes as were in the parent cell. Nuclear membrane is reformed around the each set of chromosomes. Soon the cytoplasm of cell also divides and two daughter cells arise with same number of chromosomes as in parent cell.

Q No.16. Describe the significance of Mitosis.

Ans. Mitosis is responsible for development and growth of organisms by increasing exact copies of cells. About all kinds of asexual reproduction and vegetative propagation take pace by mitosis. The production of new somatic cells, such as blood cells depends upon mitosis. The healing of wounds, repair of wear and tear within organisms also depend upon mitosis.

Q No.17. Describe Meiosis and its phases.

Ans. In Meiosis or reduction cell division a parent cell divides into four daughter cells in a way that number of chromosomes in each daughter cell is reduced to half of the parent cell (from diploid 2n to haploid n).In animals meiosis produces gametes (sperm and egg) while spores in plants. Meiosis involves two divisions.

a.      Meiosis I- First meiotic division or reduction phase.

b.      Meiosis II- Second meiotic division or meiotic mitotic phase.

a. Meiosis I- First meiotic division or Reduction phase:

1.      Prophase 1: In this phase homologous chromosomes come together and form pairs. In each pair of homologous chromosomes, there are four chromatids, since each chromosome of a pair has already doubled itself. Homologous chromosomes join to exchange their parts at certain places. This exchange is called crossing over. During crossing over new combination of genes result. Nuclear membrane disappears and spindle fibers are formed.

2.      Metaphase I: During this phase homologous chromosomes arrange themselves on the equator of spindle.

3.      Anaphase I: Chromosomes of the homologous pairs now begin to separate and move towards the opposite poles.

4.      Telophase I: At this phase chromosomes come to rest at the poles. Nuclear membranes are formed around the each set of chromosomes resulting in formation of two daughter nuclei. Then cytoplasm also divides thus two daughter cells (having haploid ‘n’ number of chromosomes) are formed.

b. Meiosis II- Second meiotic division or Equational division:

1.      Prophase II: Spindles are formed and nuclear membrane disappears.

2.      Metaphase II: Chromosomes arrange themselves on the equator.

3.      Anaphase II: Chromatids of chromosomes separate from each other and migrate to the opposite poles.

4.      Telophase II: Nuclear membrane reappears around each set of chromatids and now called chromosomes. Then cytoplasm divides to form two sets of daughter cells.

Q No. 18. Describe the significance of Meiosis.

Ans. Meiosis plays an important role in keeping chromosome number constant in species from generation to generation. When haploid sperm fertilizes with haploid ovum to form zygote, the diploid number (2n) is restored.

            Meiosis is responsible for the difference between individuals of the same species, which was due to crossing over between homologous chromosomes during Prophase I.

Q No.19. What is a tissue? Describe plant tissues.

Ans. A tissue is group of common cells which perform common function.

            There are two basic types of plant tissues:

1.      Meristematic tissues: This tissue contains cells which have ability to divide. These cells are smaller in size, thin walled and a nucleus in center. These tissues are present in root and shoot apex and help in increase of root and shoot length by adding primary tissue.

2.      Permanent tissues: Cells of these tissues are formed from meristematic cells. These cells do not divide. The walls of these cells are thick which maintain their shape.

There are two groups of permanent tissues:

I.                   Simple tissues: These are made up of one type of cells. It is further be divided into three groups on the basis of structure:

a.      Parenchyme: Consist of living cells having intercellular spaces. They are present in soft parts of plants. These tissues store food.

b.      Collenchyma: Consist of elongated cells with corners filled with cellulose and pectin. It is present in few layers under epidermis of herbaceous dicotyledons.

c.       Sclerenchyma: (Scleros=hard) Consist of very long, narrow, thick walled and lignified cells. They are very hard because of lignin so provide support to plants. They are found in xylem and hard coat fruits.

II.                Complex tissues: These are made up of more than one type of cells. They are mainly of two types:

a.      Xylem: These are consisting of thick walled elongated tissues. They have sclerenchyma vessels and fibers which conduct water and salts from soil to leaves and also provide support.

b.      Phloem: These are consisting of thin walled elongated living sieve tube like cells, which conduct food from leaves to all parts of plant.

Xylem and phloem together form vascular bundle in stem while remain separate from each other in roots.

Q No. 20. Describe animal tissues.

Ans. There are four important types of animal tissues:

1.      Epithelial tissues: Cells of these tissues occur in single layer and are closely packed together. This tissue forms surface layer under lines of tubular organs of body. Epithelial tissue occurs in the glands where it is folded.

2.      Connective tissue: These tissues provide support to other tissues and organs bind them together. They have fatty tissues which are soft and cartilages and bones are hard tissues. Blood is also a special type of connective tissue with cells suspended in fluid medium.

3.      Muscular tissues: These are made up of muscle fibers. Each muscle fiber is a elongated cell which have ability to contract and relax. These tissue are responsible for movement of body and body parts.

4.      Nervous tissues: These tissues are made up of cells called neurons or nerve cells. Nerve cell conduct message in the form of electric currents.

Q No.21. Write a note on amoeba.

Ans. Amoeba is unicellular aquatic organism found in stagnant water, pools and ponds. Its size is about 0.25 millimeter. It keeps on changing its shape.

            Structure: Cytoplasm of amoeba is covered by cell membrane. Cytoplasm is differentiated into two parts:

1.      Ectoplasm: It is an outer portion, it is clear and transparent.

2.      Endoplasm: It is an inner viscous, translucent and granular part of cytoplasm. It contains many food vacuoles, contractile vacuole and other cell organelles.

Nucleus is usually present in center but as the amoeba moves, the nucleus changes its position. Contractile vacuole removes excess water from the body. It moves and capture food particles by temporary cytoplasmic projections called pseudopodia (pseudo=false, podia=feet).

QNo.22. Write a note on Brassica (Brassica campestris).

Ans. Brassica campestris is the botanical name of mustard (Rai). Its oil is used for cooking and as hair oil and its leaves are used as vegetable (saag).

This plant consists of:

1.      Vegetative parts: Those parts which do not directly take part in sexual reproduction. Such as root, stem, leaves and branches.

2.      Reproductive parts: Those parts which take part in sexual reproduction. Such as flowers.

QNo.23: Write a note on flower of Brassica.

Ans. Brassica plant bears small yellowish flowers. The arrangement of flowers on stem is called inflorescence. The stalk on which flower is situated is called pedicle. The tip of the pedicle bears thalamus. The floral leaves are arranged in four whorls on thalamus.

1.      Calyx: This is the outer most whorl consists of four free sepals. In young flowers its colour is light greenish while yellowish in old flowers. It protects inner parts of flowers from sunlight and rain.

2.      Corolla: This is second whorl consists of four free yellow petals. Honey bees, butterflies and other insects are easily attracted due to petals.

3.      Androecium: This is third whorl consisting of not-leaf like parts. It has six free stamens which are the male reproductive part of the flower. In Brassica stamens are arranged in two circles 1. Outer circle has two small stamens and 2. Inner circle has four long stamens. Each stamen has a lower filament and a upper anther. Each anther has numerous pollen grains. There are dark green nectaries of small size at the base of androecium, which contain nectar, which is food of insects.

4.      Gynoecium: This is the fourth whorl consisting of carpels, which is the female reproductive part of the plant. In Brassica the gynoecium is formed by the union of two carpels. Each carpel is divided into three main parts:

a.      Ovary: The lower swollen part is called ovary. In ovary many ovules are present, which are ripen into seeds. The ovary ripens and converted into fruit.

b.      Style: Above the ovary carpel extends into a thin stalk called style.

c.       Stigma: Style has a swollen tip which is called stigma.

QNo. 24. Write a note on frog.

Ans. The frog (Rana tigrina) lives both in water as well as on land. It swims in water and move by jumping when on land. There are five toes in each foot while the hand has only four fingers because the thumb is rudimentary. In male frog the first finger is thicker than the other.

            Its head is directly attached to trunk because of absence of neck. Behind each eye has a tympanic membrane which helps in hearing. At the tip of snout, frog has two nostrils. The skin of frog is loose and slippery.

            Frogs are found in abundance in rainy season during which the lay eggs. They hibernate during the winter season by burying themselves into mud. This phenomenon is called hibernation or winter sleep.

QNo.25. Define respiratory system in frog.

Ans. Energy required by organisms for life processes is produced by oxidation of glucose. This process takes place in mitochondria in cell. In the presence of oxygen in cell, food is oxidized and CO_{2 is} produced as waste product. This entire process is called respiration. Respiration is divided into two phases:

1.      Gaseous exchange or Extra-cellular respiration.

2.      Cellular Respiration.

QNo.26. Describe the types of respiration in frog.

Ans. Frog has three types of respiration.

1.      Pulmonary Respiration: The gaseous exchange take place by lungs is called pulmonary respiration.

 Frog has two balloon like lungs. Their outer surface is smooth but their inner surface is folded which increase the area of gaseous exchange. The lungs are richly supplied with blood vessels. Each lung has a bronchus. Two bronchus join to form bronchi. Bronchi open into larynx. Glottis opens into the larynx.

            During respiration air is taken in by the external nostrils. It passes to buccal cavity through the internal nostril. From here it enters into glottis and passes through larynx and bronchi finally reach into lungs. From lungs oxygen is taken by the blood and CO₂ is taken out by same route.

2.      Cutaneous Respiration: Gaseous exchange carried out by the skin is called cutaneous respiration. Frog uses skin as respiratory organ during swimming and hibernation. Oxygen diffuses in blood through skin and CO₂ diffuses out from blood capillaries in skin.

3.      Buccal Respiration: The lining of buccal cavity is thin, moist and richly supplied with capillaries. Here exchange of gases takes  place between blood and air.

QNo.27. Describe the circulatory system in frog.

Ans. Frog has closed type circulatory system in which blood circulates in closed circuit of blood vessels. It consists of:

I.                   Heart

II.                Three kinds of blood vessels:

a.       Arteries: Which carry blood from heat to other body parts

b.      Veins: Which return blood to heart.

c.       Capillaries: Exchange material between tissues and blood.

QNo.28. Write a note on the heart of frog.

Ans. Heart is a conical organ located in the anterior region of the body cavity. It is enclosed in a membrane called pericardium. It contracts and expands which is called heart beat. Frog heart consists of three chambers.

1.      Right Auricle

2.      Left Auricle

3.      Ventricle

The truncus arteriosus originates from ventral side of ventricle and divides into two branches, each of which divides into three arteries.

            The oxygenated blood from lungs enters the left auricle through pulmonary veins. Deoxygenated blood from all parts of body reaches the right auricle. When the two auricles contract, the blood is pushed into single ventricle. When ventricle contracts, oxygenated blood is pushed into system arteries and blood is supplied to all parts of body while deoxygenated blood is pushed into pulmonary arteries which carry blood to lungs.

QNo. 29. Describe arterial system in frog.

Ans. A blood vessel which carries blood from heart to other parts of body is called artery. Arterial system is comprised of three main components:

1.      Pulmocutaneous Arteries: They supply deoxygenated blood to lungs and skin where it gives up CO₂ and receives oxygen.

2.      Carotid Arteries: These arteries arise from the truncus arteriosus and supply oxygenated blood to all parts of the head region such as brain, tongue, head muscles, eyes and ears etc.

3.      Systemic arteries: These vessels carry oxygenated blood to all parts of body except head and lungs.They fuse together to form aorta, which gives branches to various parts of body.

QNo.30. Describe the nervous system in frog.

Ans. The set of organs which control and co-ordinate all activities of the body is called nervous system. It is composed of two parts:

1.      Central nervous system: consists of brain and spinal cord

2.      Peripheral nervous system: Consists of nerves, which connect central nervous system with various parts of body.

The brain consists of following regions:

I.                   Most anterior region is called olfactory lobes.

II.                Behind the olfactory lobes there are two large outgrowths called cerebral hemispheres.

III.             Behind the hemispheres two other outgrowths called optic lobes are present.

IV.             The part between optic lobe and hemispheres is known as diencephalon.

V.                The last part of brain consists of cerebellum and medulla oblongata.