BIOLOGY CLASS IX BY- Mrs - PowerPoint Presentation

Slide1

BIOLOGY CLASS IX BY- Mrs. U.N.NAZNIN1. The Fundamental Unit of Life- CELL

A cell is the structural and fundamental unit of life. All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular). Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy.Cell was discovered by Robert Hooke in the year 1665.Cell is a Latin word for ‘a little room’. i. Plasma Membrane : Also known as Cell Membrane. This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The cell membrane, therefore, is called a selectively permeable membrane. ii. Cell Wall ( Plant ) Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants. When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis. iii. Cytoplasm : A large region of each cell enclosed by the cell membrane. This region takes up very little stain. It is called the cytoplasm. The cytoplasm is the fluid content inside the plasma membrane. It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell. The cytoplasm can be divided into two primary parts: the endoplasm and ectoplasm. The endoplasm is the central area of the cytoplasm that contains the organelles. The ectoplasm is the more gel-like peripheral portion of the cytoplasm of a cell.The cytoplasm functions to support and suspend organelles and cellular molecules.Many cellular processes also occur in the cytoplasm, such as protein synthesis, the first stage of cellular respiration (known as glycolysis), mitosis, and meiosis.The cytoplasm helps to move materials, such as hormones, around the cell and also dissolves cellular waste.

iv. Nucleus :The nucleus controls and regulates the activities of the cell (e.g., growth and metabolism) and carries the genes, structures that contain the hereditary information. It controls the heredity characteristics of an organism.It is responsible for protein synthesis, cell division, growth and differentiation.It is a site for transcription process in which messenger RNA (m RNA) are produced for protein synthesis.Aids in exchange of DNA and RNA (heredity materials) between the nucleus and the rest of the cell.Nucleolus produces ribosome and are known as protein factories

.v. Cell Organelles :The cellular components are called the Cell Organelles. These cell organelles are membrane-bound, present within the cells and are distinct in their structures and functions. They coordinate with their functions efficiently for the normal functioning of the cell. Few of them functions providing shape and support, whereas some are involved in the locomotion and reproduction of a cell. Depending upon the presence or absence of membrane, cell organelles can be classified into 6 different parts :

a. Endoplasmic ReticulumThe Endoplasmic Reticulum is a network of membranous canals filled with fluid. They are the transport system of the cell, involved in transporting materials throughout the cell.There are two different types of Endoplasmic Reticulum:Rough Endoplasmic Reticulum – They are composed of cisternae, tubules, and vesicles, which are found throughout the cell and are involved with protein manufacture. The rough endoplasmic reticulum manufactures membranes and secretory

 proteins. The ribosomes attached to the rough ER synthesize proteins by the process of translationSmooth Endoplasmic Reticulum – They are the storage organelle, associated with the production of lipids, steroids, and also responsible for detoxifying the cell. The smooth ER has a wide range of function including carbohydrate and lipid synthesis. It is mainly responsible for the transportation of proteins and other carbohydrates to another organelle, which includes lysosomes, Golgi apparatus, plasma membrane, etc.The Golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cisterns. These membranes often have connections with the membranes of ER and therefore constitute another portion. Golgi Apparatus also termed as Golgi Complex. It is a membrane-bound organelle, which is mainly composed of a series of flattened, stacked pouches called cisternae. This cell organelle is primarily responsible for transporting, modifying, and packaging proteins and lipid to targeted destinations. Golgi Apparatus is found within the cytoplasm of a cell and are present in both plant and animal cells of a complex cellular membrane system.(i) The main function of Golgi apparatus is to carry out the processing of proteins generated in endoplasmic reticulum. Golgi apparatus also transports protein to the different parts of cell.(ii) The Golgi enzymes present in membranous disks of cisternae carry out the modification of cargo proteins. Modification of various substances is carried out by enzymes in cisternae with the help of processes like phosphorylation and glycosylation.(iii) Polysaccharides are attached with proteins in order to form carbohydrates.c. Lysosomes : Lysosomes are a kind of waste disposal system of the cell. Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Foreign materials entering the cell, such as bacteria or food, as well as old organelles end up in the lysosomes, which break them up into small pieces. Lysosomes are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material. When the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the ‘suicide bags’ of a cell. Structurally, lysosomes are membrane-bound sacs filled with digestive enzymes. These enzymes are made by RER. Functions of Lysosomes :helps with cell metabolism by ingesting and dissolving unwanted parts of the cell, cell debris or foreign substances that have entered the cell.The digestive enzymes of their acidic interior break down large structures and molecules into simple components, and they then return the products to the cell for further use or disposal.The lysosomes essentially act as the cell's digestive system.

d. Mitochondria Mitochondria are called as the powerhouses of the cell as they produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle, found in almost all eukaryotic cells. The double membranes divide its lumen into two distinct aqueous compartments. The inner compartment is called ‘matrix’ Mitochondria are the sites of aerobic respiration in the cell,  produces energy in the form of ATP and helps in the transformation of the molecules. Mitochondria have their own circular DNA, RNA molecules, ribosomes (the 70s), and few other molecules that help in protein synthesis. Functions of Mitochondria

1.Production of ATP : The main job of mitochondria is to perform cellular respiration. This means it takes in nutrients from the cell, breaks it down, and turns it into energy. This energy is then in turn used by the cell to carry out various functions.2. Calcium Homeostasis : Mitochondrial calcium exchange is the flow of calcium in and out of a cell’s mitochondria, a process important in metabolic regulation and cell death. e. PLASTIDS: are double membrane-bound organelles found inside plants and some algae, which are primarily responsible for activities related to making and storing food. In plants, plastids may differentiate into several forms, depending upon which function they play in the cell. Undifferentiated plastids (proplastids) may develop into any of the following variants: Chloroplasts, Chromoplasts, Leucoplasts, Amyloplasts, Elaioplasts, ProteinoplastsThey helps in storage of proteins, starch and oil.They trap solar energy to manufacture food through the process of photosynthesis.They help in maintaining balance between carbon dioxide and oxygen during photosynthesisf. VACUOLES:Vacuoles are mostly defined as storage bubbles of irregular shapes which are found in cells. They are fluid-filled organelles enclosed by a membrane. The vacuole stores the food or a variety of nutrients that a cell might need to surviveThe animal and plant cell have different size and number of vacuoles. Compared to the animals, plant cell have larger vacuoles. it maintains turgor pressure within the plant cells.it acts as a storage organelle.in plants vacuoles help in maintaining the cytoplasmic pH of the cell.

Differences between Plant and Animal Cells :