Cell Biology

Class 7 | Science — Biology | Unit 4

Class 7 Unit 4 Science

Unit 4 Cell Biology

Learning Objectives

To compare the plant cell with the animal cell and understand their similarities and dissimilarities

To understand the cell as a fundamental unit of life

To know and understand the different types of Human cells and their related functions

To know the functions of different cell organelles

To compare different cell organelles, their functions and know their similarities and specialties

Introduction

Sona had a dinner, some hour later, she experienced a stomach pain and went to a clinic. After examination, the Doctor told Sona that she had eaten food contaminated with a type of bacteria which might have caused food poisoning. Bacteria are micro-organisms that can be seen only under microscope and not seen through naked eyes. Salmonella species is a bacteria that can cause food borne infection. Our earth is a beautiful place where in different types of organisms happily coexist. From minute mosses to huge conifers, invisible bacteria to huge blue whale, all have a basic unit called Cell. Let us study about the cell.

Activity 1

Do you remember the lesson studied in previous class, how will you find whether on object is living or non living? Write it down.

An object is living or non living ?

1. Form a team and work together to write down some of the functions of living things, which you can remember.

2. Do you think that an individual cell is living? Explain your answer

3. Write about various organelles of a cell which you know.

4.1 Cell as a fundamental unit of life

The building wall is made up of numerous bricks. In the similar manner, a bee hive is composed of numerous hexagonal units. Some of the organisms are represented by a single cell. Therefore, they show a simple organization. The basic functional unit of an organism is called, a cell. Structure of a cell represent the arrangement of parts or organells in a cell. Function is the activity of each part or organell in a cell. Cells are the basic building blocks of an organism. You learnt that atoms are the basic building blocks of matter in chapter three. Likewise, human body is made up of animal cells and plant is made up of plant cells.

Unicellular organisms

Some simple organisms, are made up of only one cell. They are called unicellular organisms, which can be seen with the help of a microscope. There are many single celled microscopic organisms. Have a look at the image. Chlamydomonas and an Amoeba, a single cell organisms which carryout entire functions. The body of all organisms are made up of tiny building blocks called, cells. Bacteria are also one celled unicellular organisms.

Multicellular Organism

The cells are organized into tissues, organs and organ systems in a multicellular organism. Macroscopic organisms are visible and consists of many cells. The body of macroscopic organisms involves various functions. You can see cells of onion and human through a microscope. Onion and man are examples for multicellular organism.

Cell to organism

Many cells function together to form tissues, different tissues combined together to form an organ and different organs to form an organ system, which leads to form an organism. Organisms. Many types of organ systems function together in a body, e.g. respiratory system, digestive system, excretory system circulatory system etc.

Organ System

Many organs together form an organ system, which is concerned with a specific function. For example, Respiratory system, which has organs like nostrils, nasal chamber, Vind pipe and lungs that helps in the process of respiration. In a plant, the root system consists of primary root, secondary root and tertiary root, which does the function of conduction of water , mineral and also fixation.

Organ

A collection of different tissues worked together to perform a specific function or functions is called an organ. Human body has different organs like stomach, eye, heart, lungs etc., are made up of different type of tissues. Plant has organs such as leaves, stems, and roots.

Tissue

Tissue is a group of cells, organized for a specific function. Tissues have following features like same shaped cells or different shaped cells to perform a common function. Human and other animals are made up of nervous, epithelial, connective and muscle tissues. Plants have transport, protective and ground tissues.

Cell

The cell is a basic structural and functional unit of life. Cell is the building unit of living organisms. You can see in a hand, how many types of cells are there to work together to perform its functions. So, cell is known as the basic unit of life.

Activity 2

Find out major organs that are part of the circulatory system of a human body and list out their functions.

4.2 Plant and Animal cell comparison

Why do plant cells differ from animal cells? They differ from each other because they have to perform different functions. Now you know that there are many main similarities between plant and animal cells. Let us see how they differ from one another as given in the picture (Activity 3).

4.3 Human cells related to functions

Different types of cells

Our body is made up of many different kinds of cells. Each type of cell is specialized to perform a specific function. Depending on the function, cell has specific shape, size and may have some components which other type of cells do not have. Have a look at the differences between nerve cells and red blood cells in the images. Even though there are many different types of cells, there are some components common to all type of cells. Let us take a look at this in the next section.

What's inside a cell?

Inside a cell, there are many tiny structures called cell organelles. These organelles are responsible for providing needs of the cell. They work to bring in food supplies, get rid of waste, protection and repair of the cell, and help it to grow and reproduce. Each one has a specific function to do for the cell. And, if any one organelle stops its function, then the cell is programmed to die.

Cell Structure

As we have mentioned before, all cells have some common structure. These are 1. Cell membrane 2. Cytoplasm, and 3. Nucleus (In most eukaryotic cells). The structure of a typical plant and animal cell shows following peculiarities,

Cell membrane

The boundary of an animal cell is the plasma membrane, which is also called as cell membrane.

Cell wall "Supporter and Protector"

All animal and plant cells are enclosed or surrounded by a cell membrane as you learned before. However, as you might have noticed previously that, animal cells often have an irregular shape, whereas plant cells have a much more regular and rigid shape. Plant cells have an additional layer on the outer side of the cell membrane. This is called as the cell wall, that provides a frame work for support and stability. The cell wall is formed from various compounds, the main one being cellulose. Cellulose helps to maintain the shape of the plant cell. This allows the plant to remain rigid and upright even if it grows to great heights. Each cell is interconnected with its neighbouring cells through openings called Plasmodesmata.

Description for the above picture begins, Under Plant cell picture of a tree is given, below which cross section of plant cell is given, in which nucleus, chloroplast Golgi body, mitochondria, ribosomes, cell wall and large vacuoles are seen. Below which the cell organelles found only in plant cell are given below. They are, Cell wall, The outer most covering of the plant cell. It maintains the shape and protect the cell. Chloroplast, chloroplast is a organelle, characterised by its two membranes and a high concentration of chlorophyll and carry out the photosynthesis. Large vacuole, filled with both inorganic and organic molecules, along with water to support the organelle. Under animal cell picture of a camel is given, below which cross section of animal cell in which nucleus, mitochondria, cytoplasm, endoplasmic reticulum, centriole small vacuole are seen. Below which the organelles present only in animal cell are given below, they are, Centriole, is a pair of minute cylindrical, involved in the development of spindle fibres cell division. Small vacuole, filled with both inorganic and organic molecules, along with water to support the organelle. Below these, the organelles which are found in both plant cell and animal cell are given, they are, Nucleus, is the control centre of the cell, it is the largest organelle. Ribosome, is a minute particle consisting of RNA, they synthesize polypeptides and proteins. Golgi body, is a complex of vesicles and folded membranes, involved in secretin and intracellular transport. Cytoplasm, includes all living parts of cell with in the cell membrane but excluding the nucleus. Endoplasmic reticulum a network of membranous tubules and is involved in protein and lipid synthesis. Mitochondria, are organelles, they make most of the cell's supply of adenosine triphosphate, that is ATP, a molecule that cells use as a source of energy. Their main job is to convert en ergy.

Activity 3

Description for the above picture begins, Study the pictures given and write the differences between cells that you observe in the given table. Under plant cell, picture of plant cell and following parts are labelled, golgi apparatus, chloroplast, nucleus, nucleolus, endoplasmic reticulum, cell wall and mitochondria. Under animal cell, picture of animal cell and following parts are labelled, Mitochondria, centrioles, golgi apparatus, rough endoplasmic reticulum, nucleus, nucleolus, cytoplasm, plasma membrane. Description ends.

Structure and functions of specialised cells

Structure of epithelial cells, they are mostly flat and columnar in shape,

Function of epithelial cells They cover the surface of the body for protection.

Structure of muscle cells, they are long and spindle shaped,

function of muscle cells, they can control and relax allowing the cell for movement.

Structure of nerve cell, the body of nerve cell is branched with an elongated nerve fiber.

Function of nerve cells are specialised to carry and conduct messages that coordinate the functions of the body.

Structure of red blood cells are round, biconcave and disc shaped.

Functions of red blood cells, they carry oxygen and collect carbon dioxide from various part of the body.

Do You Know?

Stem Cells , Stem cells are quite amazing as they can divide and multiply while at the same time with their ability to develop into any other type of cell. Embryonic stem cells are very special as they can become absolutely any type of cell in the body, for example, blood cell, nerve cell, muscle cell or gland cell. So they are utilized by the Scientist and Medicos, to cure and prevent some diseases like Spinal cord injury.

Cytoplasm, I am the "Area of Movement".

When you look at the temporary mounts of an onion peel, you can see a large region of each cell an enclosed by the cell membrane. This region takes up very little stain. It is called the cytoplasm. The cytoplasm includes all living parts of the cell with in the cell membrane, excluding the nucleus. The cytoplasm is made up of the cytosol and cell organelles. The cytosol is a watery, jelly- like medium made up of 70 % to 90% water and usually colourless. Cell organelles and structures present in a cell are endoplasmic reticulum, vacuole, ribosome, golgi body, lysosome, mitochondria, centriole, chloroplast, surrounded by plasma membrane and cell wall.

Protoplasm versus Cytoplasm

In particular, the material inside and outside the nuclear membrane is known as Protoplasm. The fluid inside the nucleus is known as the nuclear fluid or nucleoplasm and outside the nucleus is called as cytoplasm.

Inside the cytoplasm

Mitochondria "Power house of the Cell".

Do you remember learning about the food as the energy source for the body? Just as wood is burnt to release the stored potential energy to make a fire to heat some water. The food that you ate to be broken down in order to release the energy which can be used by your body to function. Mitochondria are responsible to do this function. Very active cells have more mitochondria than cells that are less active. Which type of cell, do you think, will have more mitochondria, a muscle cells or a bone cell? Mitochondrian is an oval or rod shaped double membrane bounded organelle. Aerobic respiratory reactions take place with in the mitochondrion to release energy. So it is known as "the Power House" of the cell. The energy produced within the mitochondrion is used for all the metabolic activities of the cell.

Chloroplast "Food Producers".

Do you notice the green organelles present in plant cells and absent in animal cells. Chloroplasts are the only cell organelles that can produce food from the sun energy. Only plants with chloroplast are able to do photosynthesis because they contain the very important green pigment, chlorophyll. Chlorophyll can absorb radiant energy from the Sun and convert it to the chemical energy which can be used by the plants and animals. Animal cells lack chloroplasts and are unable to do photosynthesis.

Observing chloroplast in algae Collect some algae from pond and separate out thin filaments of them. Place a few filaments on a slide. Observe it under the microscope. Take the help of given figure and draw the picture of chloroplast that you have observed under the microscope. Chloroplast is a type of plastid. which are present only in plant cells. Plastids are mainly of two types, chromoplasts (coloured) and leucoplasts (colourless).

Do You Know?

Various range of these plastids impart different colours to various parts of plant. Chromoplast impart colour to flower and fruits. As fruits ripen, chloroplasts change to chromoplasts. Starch is converted to sugar.

Golgi Complex, I need a break

Membrane bounded sacs are stacked on top of the other with associated secretory vesicles are collectively known as Golgi complex. Functions of Golgi complex are the production of secretory substances, packaging and secretion. This is the secret behind the change in the colour and taste of fruits.

Lysosome "Suicidal Bag".

Everything I touch, I destroy. You will find organelles called as lysosomes, which are very small to view using a light microscope. They are the main digestive compartments of the cell. They lyse a cell, hence they are called "suicidal bag".

Centrioles

They are generally found close to the nucleus and are made up of tube like structures. Centrioles or centrosomes are present only in animal cells and absent in plant cells. It helps in the separation of chromosomes during cell division.

Endoplasmic reticulum, You guys, be quiet, I have so much work to do

It is an inter membranous network made up of flat or tubular sacs within the cytoplasm. Endoplasmic reticulum is of two types. They are rough endoplasmic reticulum and smooth endoplasmic reticulum. Rough endoplasmic reticulum are rough due to the ribosomes attached to the membrane, which helps in the synthesis of protein. Smooth endoplasmic reticulum. It is a network of tubular sacs without ribosomes on the membrane. They play a role in the synthesis of lipids, steroids and also transport them within the cell.

Nucleus, Everyone do what I say. Acting like the "Brain" of the cell

Plant and animal cells have a nucleus inside the cytoplasm. It is surrounded by a nuclear envelope. One or two nucleolus and the chromatin body are present inside the nucleus. During cell division, the chromatin body is organised into a chromosome. Storage of genetic material and transfers heredity characters from generation to generation are the functions of chromosome.

Functions of Nucleus

In controls all the processes and chemical reactions that take place inside the cell.

Inheritance of character from one generation to another.

Activity 3

Summarise what you have learnt

Now you have studied the internal structure of a cell. Let us summarise what we have learnt so far

Complete this table by filling the main function of each of the cell structures in the following table.

Cell structure	Functions
1, cell membrane
2, cell wall
3, cytoplasm
4, mitochondria
5, vacuole
6, chloroplast
7, endoplasmic reticulum

Do You Know?

Red blood cells Red blood cells do not contain a nucleus. Without a nucleus, these cells die quickly, about two million red blood cells die every second, Luckily, the body produces new red blood cells every day.

POINTS TO REMEMBER

Cells are the basic structural and functional units of all living organisms.

Cells are microscopic and can be seen only under a microscope.

Cell membranes are selectively permeable, which means they only allow certain substances to pass in and out of the cell.

Plant cells have a cell wall around the cell membrane that is rigid and provides support and protection to the cell content.

The Cytoplasm includes the organelles and the cytosol.

The Cytosol is the jelly like medium, in which many chemical reactions take cell.

Everything inside the cell membrane, except the nucleus, is considered to be the cytoplasm.

Mitochondria are responsible for cellular respiration, which releases the energy from the food.

Plants have chloroplasts with chlorophyll pigments to produce food by photosynthesis.

Stem cells are cells that have the ability to divide and develop into many different types of the cell.

A group of different tissues makes up an organ.

Organs working together in groups form a systems or organ systems.

Organ systems make up an organism, such as a human.

Evaluation

Exercise I. Choose the correct answer

1. Basis unit of life.

A) Cell B) Protoplasm C) Cellulose D) Nucleus

2. I am the outer most layer of an animal cell. Who am I?

A) Cell wall B) Nucleus C) Cell membrane D) Nuclear membrane

3. Which part of the cell is called the brain of the cell?

A) Lysosome B) Ribosome C) Mitochondria D) Nucleus

4. _______ helps in cell division

A) Endoplasmic reticulum B) Golgi complex C) Centriole D) Nucleus

5. Suitable term for the various components of cell is _______.

A) Tissue B) Nucleus C) Cell D) Cell organelle Exercise II. Fill in the Blanks

1. The jelly like substance present in the cell is called .

2. I convert the Solar energy into food for the plant. Who am I? .

3. Mature Red blood cell do not contain a .

4. Unicellular organisms can only be seen under a .

5. Cytoplasm plus nucleoplasm is equal to .

Exercise III. True or False. If false give the correct answer 1. Animal cells have a cell wall. 2. Salmonella is a unicellular bacteria. 3. Cell membrane is fully permeable. 4. Only plant cells have chloroplasts. 5. Human stomach is an organ. 6. Ribosomes are small organelles with a membrane. Exercise IV. Match the following

1 Transporting channel
2 Suicidal bag
3 Control room
4 Power house
5 Food producer

Options: Nucleus, Endoplasmic reticulum, Lysosome, Chloroplast, Mitochondria

Exercise V. Analogy

1. Bacteria is to microorganism, mango tree is to .

2. Adipose is to tissue, eye is to .

3. Cell wall is to plant cell , centriole is to .

4. Chloroplast is to photosynthesis , mitochondria is to .

Exercise VI. Choose the correct alternative from the following

1. Assertion (A) Tissue is a group of dissimilar cells. Reason (R) Muscle is made up of Muscle cell.

a. Both Assertion and Reason are true b. Both Assertion and Reason are false c. Assertion is true but Reason is false. d. Assertion is false but Reason is true.

2. Assertion (A) : Majority of cells cannot be seen directly with naked eye because. Reason (R) : Cells are microscopic.

a. Both Assertion and Reason are true b. Both Assertion and Reason are false c. Assertion is true but Reason is false. d. Assertion is false but Reason is true. Exercise VII. Very short answer

1. What are the functions of cell wall in plant cell?

2. Which organelle uses energy from sunlight to make starch?

3. What are the main things in a nucleus?

4. What does cell membrane do?

5. Why lysosomes are known as scavengers of the cell?

6. Teacher said "A virus is not an organism" Do you agree with this statement or not? Explain Why?

Exercise VIII. Give short Answer

1. Why the cell is very important for us?

2. Distinguish between the following pairs Smooth Endoplasmic reticulum and Rough Endoplasmic reticulum, Cell wall and cell membrane, Chloroplast and mitochondria

3. Write correct sequence from cell to organism?

4. Write a short note on nucleus.

5. Classify the following terms into cells, tissues, organs and write in the tabular column given below. Neuron, Lungs. Xylem, brain, adipose, Leaf, R B C, W B C, hand, muscle, heart, ovum, squamous, phloem, cartilage.

Cells	Tissues	Organs

6. On the lines given below, write about what you have learned from the activities done in this lesson. Let me tell you about some of the important things I have learned about cells. First, I will start with lines .

Exercise IX. Give long answer

1. Write about any three organelles in detail.

2. In a situation, how to explain, while your friend ask what is this, never seen before?

3. Compare the plant cell and the animal cell and complete the illustration given below.

Exercise X. Higher order thinking question

Virus is called Acellular. Why?

📝 Summary

1. Cell is the basic functional unit and building block of all organisms, just as bricks make up a wall and atoms make up matter.
2. Organisms are classified as unicellular (single-celled like bacteria, Chlamydomonas, and Amoeba) or multicellular (many-celled like onion and humans).
3. In multicellular organisms, cells are organized hierarchically: cells form tissues, tissues form organs, organs form organ systems, and organ systems form complete organisms.
4. Plant cells and animal cells have both similarities and differences in structure and function, with each containing various organelles that perform specific functions.
5. Different types of human cells exist with specialized functions, and understanding cell organelles helps us comprehend how cells carry out life processes.