Standard IX

NATIONAL ANTHEM

PREFACE Dear Students, Biology is a branch of science that deals with living organisms and their vital processes. You will certainly be surprised to learn how the human brain, nerves and hormones act together to co-ordinate the activities of the human body. This text includes interesting applications and conveys the major themes of biology, with content that is meaningful and easy to understand. The book is designed to demonstrate biology concepts and to promote scientific literacy. The student’s role is pivotal in the process of construction of knowledge. This Science textbook is only a resource in the learning process. Teachers and supplementary materials will help you in the creation of knowledge. 'Samagra', the education portal and technology enabled Q R Code printed textbooks would definitely make your learning activity in classrooms easy and joyful. The National Skills Qualifications Framework, the current relevance of Disaster Management and the possibilities of I.C .T. have also been considered while modifying the textbook. Let all this be beneficial for you in the learning of Science by joyfully participating in life related learning experiences that impart knowledge and happiness. Love and Regards, Abhirami S EDITOR

CONTENT

UNIT 1 Plant growth and meristem UNIT 2 Cell division UNIT 3 Mitosis

UNIT 1 PLANT GROWTH

PLANT GROWTH Did you notice the conversation between the children? Is the growth of a tree and that of a man of the same age similar?

GROWTH Growth is regarded as one of the most fundamental and conspicuous

characteristics

of a living being.

Growth can be defined as an irreversible permanent increase in size of an organ Or it’s parts or even of an

individual cell. Generally, growth is accompanied by metabolic processes ( both anabolic and catabolic ),

that occur at the expense of energy. Therefore, for example, ex pansion of a leaf is growth.

PLANT GROWTH Most plants grow in the ground, with stems in the air and roots below the surface. Some float on water. The root part absorbs water and some nutrients the plant needs to live and grow

Illustration 1.1 Germination and seedling in Apple

Plants

grow

due

to

the

rapid

division

and

differentiation of meristematic cells. Meristematic cells are special type of cells that have the capacity for continuous division. Plants can grow through out their life due to the presence of these cells.

MERISTEM The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. Differentiated plant cells generally cannot divide or produce cells of a different type.



Where are the meristematic tissues located in plants? Analyse the illustration 1.2 based on the indicators and prepare notes.

Illustration 1.2 Different kinds of meristem

Indicators 1.Why is that growth in plants is localized only at certain parts? 2.The stem of monocots increase in length faster than dicots. Why? 3.The stem of monocots does not increase girth beyond an extent. Why?

Activities 1) Where are the meristematic cells seen in plants? Observe Illustration 1.2 Discuss this on the basis of indicators and prepare a short note in the science diary 2)Observe the diagram and find out the answers. a)Identify the figure.

b) Label the parts marked. c)Write the functions of parts marked

UNIT 2 CELL DIVISION

Cell division

Cell division happens when a parent cell divides into two or more cells called daughter cells. Cell division usually occurs as part of a larger cell cycle. All cells reproduce by splitting into two, where each parental cell gives rise to two daughter cells.

These newly formed daughter cells could themselves divide and grow, giving rise to a new cell population that is formed by the division and growth of a single parental cell and its descendant. In other words, such cycles of growth and division allow a single cell to form a structure consists of millions of cells.

Types of cell division

There are two distinct types of cell division out of which the first one is vegetative division, where in each daughter cell duplicates the parent cell called mitosis. The second one is meiosis, which divides into four haploid daughter cell.

Types of cell division 1. MITOSIS

2. MEIOSIS

MITOSIS Mitosis is the type of cell division that helps in the growth of the body. This is a process by which a mother cell divides into two daughter cells. During mitosis, division of nucleus takes place first. This phase is known as karyokinesis.

MEIOSIS In this type of cell division, sperm or egg cells are produced instead of identical daughte r cells as in mitosis.

CELL CYCLE

The sequence of events by which a cell duplicated it’s genome, synthesis the other constituents of the cell and eventually divides into two daughter cells is termed cell cycle .

PHASES OF CELL CYCLE There are two primary phases in the cell cycle: 1 ) Interphase : This phase was thought to represent the resting stage between subsequent cell divisions, but new research has shown that it is a very active phase. 2) M Phase (Mitosis phase): This is where the actual cell division occurs. There are two key steps in this phase, namely cytokinesis and karyokinesis

Interphase consist of: G1 PHASE S PHASE G2 PHASE

ACTIVITIES

1)Define cell cycle

2) Name the phases of cell cycle? 3)What is mitosis?

4)What is meiosis?

5) Complete the cell cycle diagram by writing the correct name of a phase on each line .

UNIT 3 MITOSIS

Cell division is the driving process of reproduction at the cellular level. Most eukaryotic cells divide in a manner where the ploidy or the number of chromosomes remains the same, except in the case of germ cells where the number of chromosomes is halved.

MITOSIS

Mitosis is the phase of the cell cycle where the nucleus of a cell is divided into two nuclei with an equal amount of genetic material in both the daughter nuclei. It succeed s the G2 phase and is succeeded by cytoplasmic division after the separation of the nucleus

Stages in mitosis

PROPHASE I

The completion of the prophase is characterised by the initiation of the assembly of the mitotic spindle, the microtubules and the proteinaceous components of the cytoplasm that help in the process. The nuclear envelope starts disintegrating.

PROPHASE 2

In the prometaphase, the nuclear envelop disintegrates. Now the microtubules are allowed to extend from the centromere to the chromosome. The microtubules attach to the kinetochores which allow the cell to move the chromosome around.

METAPHASE

At this stage, the microtubules start pulling the chromosomes with equal force and the chromosome ends up in the middle of the cell. This region is known as the metaphase plate. Thus, each cell gets an entire functioning genome.

ANAPHASE

The splitting of the sister chromatids marks the onset of anaphase. These sister chromatids become the chromosome of the daughter nuclei. The chromosomes are then pulled towards the pole by the fibres attached to the kinetochores of each chromosome. The centromere of each chromosome leads at the edge while the arms trail behind it.

TELOPHASE

The chromosomes that cluster at the two poles start coalescing into an undifferentiated mass, as the nuclear envelope starts forming around it. The nucleolus, Golgi bodies and ER complex, which had disappeared after prophase start to reappear.

CYTOKINESIS

Telophase is followed by cytokinesis, which denotes the division of the cytoplasm to form two daughter cells. Thus, it marks the completion of cell division.

Functions of Mitosis Mitosis helps i n the development of an

organism.

In

singlecelled

organisms, mitosis is the process of asexual reproduction. Mitosis helps in the replacement of damaged tissues. The cells near the damaged cells begin mitosis when they do not sense the neighbouring cel ls. The dividing cells reach each other and cover the damaged cells.

Activities 1. In which phases does the chromatin reticulum become chromosome? 2. What change occur in telophase? 3. Distinguish between prophase and telophase? 4. Explain interphase with it’s stages. 5. With neat labeled diagram compare metaphase and anaphase of mitosis? 6. Match the following