Concept 1 the Cell as a System (G6th First Term) - PDF

AlTamayuz in Science G6th First Term Prepared by Dr/ Zeinab Salah ‫للتواصل وحجز مجموعات اﻷونﻼين‬ Tel: 01014731686 Dr/ Zeinab Salah 0 Tel: 01014731686 ...

AlTamayuz in Science G6th First Term Prepared by Dr/ Zeinab Salah ‫للتواصل وحجز مجموعات اﻷونﻼين‬ Tel: 01014731686 Dr/ Zeinab Salah 0 Tel: 01014731686  Unit 1: What is a System? Concept 1: The Cell as a System The Cell  The cell: is the main building unit of the living organism’s body that carries out all its vital activities (growth, reproduction, motion, ….).  The cell is considered as the main building unit of life, structure and function of all living organisms on Earth.  Cells are found only in living organisms and not in non-living things. Characteristics of cells  Living organisms are different in shape and structure but all of them are made up of cells.  Cells of living organisms may differ in number, size, shape, and structure. 1) Number of cells  Living organisms are divided into: 1) Unicellular organisms: their bodies consist of one cell only such as bacteria. 2) Multicellular organisms: their bodies consist of many cells such as humans, animals and plants.  The human body contains about 40 trillion cells.  Living organisms grow and reproduce as a result of increasing the number of cells that make up their bodies but not increasing in size.  Increasing in cell number of organism means formation of new cells that are formed from cells that were already existed in its body. Dr/ Zeinab Salah 1 Tel: 01014731686  2) Size of cells  Most cells are tiny structures that can’t be seen by naked eyes so we need a special device to see it called microscope.  Example: The length of animal cells and plant cells ranges between 0.1 and 0.005 mm, while the length of bacterial cell is less than 0.005 mm.  Some cells may be too large and can be seen with naked eye such as unfertilized bird egg that contains only one big cell. 3) Shape of cells  Animal and plant cells are different in shape.  Also the cells of one living organism are not identical.  Ex. Human body contains different types of cells that differ in shape and function such as nerve cells, muscle cells, and blood cells). 4) Structure of cells  Cells can differ in structure and function as following:  Some cells don’t contain nucleus such as red blood cells.  All cells have a cell membrane but not all cells have a cell wall.  Ex. plant cells have a cell wall and a cell membrane, while animal cells have a cell membrane and don’t have a cell wall. Cell needs  The basic needs of a cell are similar to the needs of all organisms as: 1) Oxygen and nutrients to get energy needed to grow and survive. 2) Water. 3) Get rid of waste materials.  The cell membrane keeps the water balance on both sides of the membrane (inside and outside the cell) as it: 1) Allows water to enter the cell to survive. 2) Allows excess water to go outside the cell, because when much water enter the cell it will swell until it bursts. Dr/ Zeinab Salah 2 Tel: 01014731686 Brief history of the cell  Robert Hooke is the first scientist who discovered tiny particles under microscope and named them with cells.  Modern microscopes help scientists to discover more information about cells (such as structure and function of cells) and they exchange this information between them.  The Structure of microscope:  The microscope consists of many parts that help scientists to see magnified images for cells.  Objective (focal) lenses are one of the components of the microscope that have different focusing (magnifying) power as following: 1) When using low power objective lens, you see the cell in small size. 2) When using high power objective lens, you see the cell in bigger size.  The microscope also contains coarse focus and fine focus to make the image of the sample very clear under the microscope. Dr/ Zeinab Salah 3 Tel: 01014731686 Structure of multicellular organism’s body  The structure of most multicellular organisms is organized in 5 levels: 1) Cell: the smallest unit of life. 2) Tissue: composed of a group of similar cells doing the same function. 3) Organ: composed of a group of different tissues work together to do its function. 4) System: composed of a group of different organs work together to do specific function. 5) Whole body: composed of a group of different systems work together. Structure (parts) of a cell  All cells contain different tiny structures inside the cells called organelles.  Each type of organelles has a special function.  Most of animal and plant cells are composed of common organelles (to control, organize, and maintain the cell) which are: cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and vacuole.  Plant cells differ from animal cells in the presence of: 1) Cell wall: the rigid outside layer that made up of cellulose material and surrounds the plant cell from outside and gives the cell a definite shape. 2) Chloroplasts: special organelles in the plant cell contain green tiny grains called the pigment chlorophyll that absorbs energy from sunlight to help plant to make photosynthesis process.  Note: animals don’t have cell walls but they have other ways of keeping their shape such as:  Some animals have bones.  Insects have an exoskeleton (a hard, shell-like covering). Dr/ Zeinab Salah 4 Tel: 01014731686 Common cell organelles 1) Cell membrane (plasma membrane)  The outer lining of the cell.  It surrounds the cell from outside to protect it.  It controls the substances that enter or leave the cell through property called selective permeability.  Selective permeability: means that cell membrane allows some substances to pass through into the cell while prevent others from entering the cell. 2) Cytoplasm  Cytoplasm is the gelatinous (thick) liquid inside the cell in which all organelles float. 3) Nucleus  Nucleus found in the center of the cell.  It controls all the cell activities such as formation of proteins and cell division to form new cells. 4) Mitochondria  Mitochondria are one of the organelles in the cell that known as powerhouses of the cell.  They provide cell with needed energy that help the cells make their functions through a process called cellular respiration.  Cellular respiration: It's a process of using oxygen gas to get chemical energy from food (converting sugar inside cell into energy). Dr/ Zeinab Salah 5 Tel: 01014731686  5) Endoplasmic reticulum  Endoplasmic reticulum is one of the organelles in the cell that help in assembling (collecting) and transporting proteins inside the cell to build and repair the cell. 6) Golgi apparatus  Golgi apparatus is one of the organelles in the cell that help in packing and transporting different materials between the cells and out of the cells. 7) Vacuoles  Vacuoles are one of the organelles in the cell that are saclike structures used for the storage of nutrients, water, and wastes.  Animal cells contain small vacuoles, while plant cells contain one large vacuole because the plant stores a large amount of water in the vacuole. Dr/ Zeinab Salah 6 Tel: 01014731686  Planning a cell city Dr/ Zeinab Salah 7 Tel: 01014731686 Comparison between animal and plant cell P.O.C. Animal cell Plant cell Similarities cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus Differences Definition The building unit of animal The building unit of plant body. body. Vacuole Many small vacuoles. One big sap vacuole. Cell wall Absent, so it doesn’t have a Present, so it has a definite definite shape. shape. Chloroplasts Absent, so animals can’t Present, so plants can make make their own food. their own food. Careers and Cell biology  Cell biologists: are scientists who study cells by using microscopes, to magnify cells as the diameter of animal cell is about 0.001 cm.  Cell biologists work with doctors to study how cell work, divide, respond to different variant and respond to medications.  Cell biologists work with agriculture to study plant cells and how they respond to different factors.  Cell biologists analyze data and exchange their findings between them.  Cells are usually clear and colorless, so it is difficult to see their structures under microscope.  Stains or dyes are used to make the structures of cells more visible.  Different types of stains are used such as methylene blue dye that make only one part of the cell more visible which is the nucleus.  Scientists have built a 3D microscope that shows a live cell in 3D (top, sides, and layers), as it takes pictures of cell in layers.  This helps biologists to discover more about cells and their division.  Also this help doctors to treat cancer which is caused by cells that divide too quickly. Dr/ Zeinab Salah 8 Tel: 01014731686