Cells and Organisation
Learning Objectives:
To know the functions of the cell wall, cell membrane, cytoplasm, nucleus, vacuole, mitochondria and chloroplasts.
To know the similarities and differences between plant and animal cells.
To understand cells as the fundamental unit of living organisms.
Introduction
This is the introductory unit to cells and their organisation within both plants and animals.
Session One – How to Use a Microscope
What are the smallest objects that you have ever seen images of?
Take a look at these.
Resources:
- microscopes
- pre-prepared slides
- Objects to view through the microscope
- blank slides
Parts of a light microscope
- Test yourself here.
- Learn how to use a light microscope here.
- Demonstration with prepared slides.
- Preparation of new slides.
- Draw cells.
- Identify cells from slides.
- Compare cells – identify differences and similarities between drawings and observations.
Activity One:
Label the parts of the microscope. You can use this or you can draw your microscope.
Extension: Research the difference between a light and an electron microscope. Start here.
Session Two – Animal Cells
Animal cells are distinct from plants, as they lack cell walls and chloroplasts and have smaller vacuoles. Due to the lack of a cell wall, animal cells can transform into a variety of shapes.
Structure of animal cells.
- Find out more here – select animal cell.
Cell membrane
- The cell membrane separates the interior of all cells from the outside environment and protects the cell from its environment.
- The cell membrane controls the movement of substances in and out of cells and organelles.
- The cell membrane is selectively permeable and able to regulate what enters and exits the cell.
Nucleus
- The nucleus (from Latin meaning kernel or seed) is an organelle found in eukaryotic cells.
- The nucleus has a double membrane that encloses the entire organelle and isolates its contents from the cytoplasm.
- The cell nucleus contains all of the cell’s DNA, except for a small fraction of mitochondrial DNA.
- The nucleus controls the activities of the cell and is, therefore, the control center of the cell.
Cytoplasm
- The cytoplasm is all of the material within a cell, enclosed by the cell membrane, except nucleus.
- The main components of the cytoplasm are cytosol – a gel-like substance, and the organelles .
- The cytoplasm is about 80% water and usually colorless.
Mitochondria
- Mitochondria are organelles (tiny organs), or parts of a eukaryote cell. They are in the cytoplasm, not the nucleus.
- They make most of the cell’s supply of adenosine triphosphate (ATP), a molecule that cells use as a source of energy. Their main job is to convert energy. They oxidise glucose to provide energy for the cell. The process makes ATP, and is called cellular respiration. This means mitochondria are known as “the powerhouse of the cell”.
- In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as cell death, the control of the cell division cycle, and cell growth.
Function of organelles in animal cells.
- An organelle is a specialized unit within a cell, that has a specific function. The name organelle comes from the idea that these structures are parts of cells, as organs are to the body, hence organelle (small organs).
Activity Two:
Label and colour the animal cell diagram (or draw your own!)
Session Three – Plant Cells
Plant cells are present in green plants. Plant cells have cell walls, constructed outside the cell membrane. Different plant cells form the tissues of roots, stems, leaves, flowers, and reproductive structures, each of which may be composed of several cell types.
Structure of plant cells.
- Find out more here – select animal cell.
Cell wall
- A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid.
- It provides the cell with protection, and also acts as a filtering mechanism.
- Cell walls are found in algae, fungi and plants, but not in animals.
- A major function is to act as pressure vessels and stop the cell from over-expanding when water enters.
Chloroplasts
- Chloroplasts are organelles that conduct photosynthesis. This is where the chlorophyll captures the energy from sunlight.
- Chloroplasts carry out a number of other functions including the immune response in plants.
- The number of chloroplasts in plant cells varies from one (algae) to 100 (wheat).
Vacuole
- A vacuole is an organelle which is present in all plant and fungal cells and some animal and bacterial cells.
- Vacuoles are enclosed and filled with water containing inorganic and organic molecules including enzymes in solution.
Function of organelles in plant cells.
- The function of vacuoles varies greatly according to the type of cell in which they are present, having much more importance in the cells of plants than animals. Some functions include:
- Isolating materials that might be harmful to the cell.
- Containing waste products.
- Containing water in plant cells.
- Exporting unwanted substances from the cell.
- Allows plants to support structures such as leaves and flowers due to the pressure of the central vacuole.
- By increasing in size, allows the germinating plant or its organs (such as leaves) to grow very quickly and using up mostly just water.
Activity Three:
Label and colour the plant cell diagram (or draw your own!)
Session Four – Unicellular Organisms
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells.
Unicellular organisms include bacteria, archaea, protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, possibly emerging 3.8–4 billion years ago.
Although some unicellular organisms live in colonies, they are not specialised cells with differing functions. Each individual cell must carry out all life processes to survive.
Multicellular organisms have cells that depend on each other to survive.
More information about unicellular organisms here.
Structure of a unicellular organism.
- Find out more here – select animal cell.
Cilia
- The first type are short, hair-like projections arranged in longitudinal rows throughout the body that helps in their movement.
- The others are long and fewer in number, present at the posterior end of their body that helps to catch and eat prey.
Cytoplasm
- The jelly-like fluid that fills up the entire cell.
- The outer thin, dense and clear layer of cytoplasm that is bound to pellicle on one side is called ectoplasm.
- Below this lies the endoplasm, a fluid-type, granular cytoplasm that contains the majority of cell organelles.
Nucleus
a) Macronucleus: Kidney like or ellipsoidal in shape that is densely packed with DNA.
b) Micronucleus: Found close to the macronucleus, it is a small and compact structure, spherical in shape, and controls reproduction.
Vacuoles
a) Contractile Vacuole: It collects fluids from the entire cell and expels them out of the cell.
b) Food Vacuole: It contains digestive enzymes that help in the digestion of food.
Oral Groove
- A long, narrow depression found in the anterior side of the cell, lined with cilia which beat continuously to draw food inside the cell.
- Also called the vestibulum.
Anal Pore
- All the undigested food gets eliminated through the anal pore.
- Also known as cytopyge, cell anus, or cytoproct.
Activity Four:
Label and colour the unicellular organism diagram (or draw your own!)
Session Five – Comparison of Unicellular and Multicellular Organisms
There are many similarities between unicellular and multicellular organisms. Even though organisms such as bacteria only have a single cell, the parts of the cell perform all the same basic functions of an animal or plant:
- They take in nutrients and expel them.
- They eliminate waste.
- They move.
- They catch food.
- They have DNA.
Activity Five:
Identify the features of unicellular and multicellular organisms.
Session Six – Specialized Cells
The cells of multicellular organisms become specialized so that they can perform a set of particular roles or functions.
The simplest and way to think about these cells is like the building blocks whose unique working combination makes the human body function how it is meant to. There are many kinds of cells. Some of them are grouped together and make up different body parts, such as the case of body tissue, for example. But others carry out rather more specialized and complex tasks or functions.
These specialized cells carry out their functions because they were specifically designed to do so. It is important to note that each of them has been formed separately and they function autonomously. This is because each one of them has a specific function to perform that cannot be interfered with.
Learn about specialized cells and take a quiz here. (The video will not work in all countries.)
Activity Six:
Here is a list of some specialized cells:
- Neurons
- Muscle cells
- Sperm cells
- Red blood cells
- Leukocyte cells (white blood cells)
Here are images of the specialized cells above.
Create an explanatory poster or trifold leaflet about specialized cells. Draw an example of each cell, label it, and write a very short description of its function. You can add other specialized cells if you wish.
Here is an example of a poster about Stem Cells. Your poster is about Specialized Cells.
Cell Day Deliverables.
- Activity One: Label the parts of the microscope.
- Activity Two: Label and colour the animal cell diagram.
- Activity Three:Label and colour the plant cell diagram.
- Activity Four: Label and colour the unicellular organism diagram.
- Activity Five: Identify the features of unicellular and multicellular organisms.
- Activity Six: Create an explanatory poster or trifold leaflet about specialized cells.
- Cover Page
- Contents
Assessment Grid.
Wrap up!
Cells Quiz
What do you know about cells? Test your knowledge here.
