KS3
Living Organisms
Have you ever wondered why a leaf is structured the way it is or what microscopic living organisms look like?
This topic will teach you about specialised cells and their roles in the body system.
Animal cells
Animal cells contain a nucleus, cytoplasm, a cell membrane, ribosomes and mitochondria.
Animal and plant cells
There are a few differences between animal and plant cells. Each are made up of different structures called organelles. Each organelle has its own function.
Nucleus
The nucleus controls what happens in the cell and carries the important genetic information called DNA (deoxyribonucleic acid).
Cell Membrane
The cell membrane is the cells outer layer, is flexible and decides what travels in an out of the cell.
Mitochondria
Mitochondria use glucose and oxygen to produce energy, carbon dioxide and water through aerobic respiration. When we model a cell, we usually draw three or four organelles, but there are actually between 1000 and 2500, which take up roughly twenty-five per cent of the cell's volume.
Cytoplasm
The cytoplasm is a jelly-like substance mostly made up of water, where chemical reactions happen.
Ribosomes
This is where protein synthesis occurs.
Plant cells
The organelles of a plant cell are the same as an animal cell, but with a few extras. A cell wall, vacuole and chloroplasts.
Cell Wall
Providing strength to the plant, the cell wall is tough and contains cellulose.
Vacuole
Helping to hold the cells shape, is the vacuole. It's filled with a liquid called sap keeping the cell rigid.
Chloroplasts
The leaves and stems of plants have cells that contain chloroplasts. They contain the green pigment chlorophyll which is where photosynthesis occurs.
Cells under a microscope
Cells are around 0.01mm in length, and human eyes can only see down to 0.05mm, so without the help of a microscope, viewing cells would be quite hard.
When using a light microscope, the magnification of the eyepiece lens gets multiplied by the objective lens to give total magnification.
The eyepiece lens is usually x10 magnification, and the objective lenses can be, x4, x10, x40, and x100. The x100 objective lens uses immersion oil to help with resolution.
Total magnification = eyepeice lens x objective lens.
Total magnification = x10 x x40
Total magnification = x400
Using a microscope
Using a microscope is easy. Follow the steps below to learn how. Then use your microscope to discover lots of wonderful living organisms.
Step 1
Carry (with both hands) the microscope using the arm and base to the location required. Plug it in making sure the illuminator is working reducing the light intensity to start with
Step 2
Bring the stage as close to the objective lens as possible, making sure you are using the smallest objective lens (normally x4)
Step 3
Place slide into the stage clip and move the stage slowly away from the lens using the course focus.
Step 4
When an image appears, switch over to the fine focus, giving a higher resolution.
Step 5
Make a drawing of the image. Use a pencil don't worry about shading or anything fancy, just draw the outlines of the specimen your observing (Don't forget to write the magnification down)
Step 6
Increase magnification. The image should appear straight away but will be out of focus, so repeat steps 4-6 until you cannot increase magnification any further.
Types of microscope
There are two types of microscopes. The first is the light microscope which you will use in school, the second is an electron microscope. The electron microscope is able to see cells to a higher magnification and resolution, but will only give black and white images. The light microscope shows images in colour but will require stains to help see colourless samples. The electron microscope is used a lot in the diagnosis of different diseases and costs £250,000 for a cheap model.
Electron microscope
This image is from an electron microscope and is a picture of cilia (found in the lungs, trachea and digestive system) at x20,000 magnification.
Specialised cells
Animals have specialised cells that are important for different roles. Click on each of the cells to learn more about them and their roles.
A red blood cell has no nucleus and is packed with haemoglobin.
It is concave shape on both sides to maximise surface area allowing oxygen to be absorbed faster.
The nervous system consists of nerve cells. Nerve cells transmit electrical signals at high speeds throughout the body, allowing quick responses to the environment.
There are three types of nerve cells, Sensory, relay, and motor. Some nerve cells are over 1 meter long and use nerve endings to pass
on messages or stimulate other cells.
To prevent miscommunication, they have a myelin (fatty) sheath around them, which acts as an insulator similar to an electrical wire having a plastic coating.
The location of ciliated cells is in the uterus and airways. They are cells with hair-like structures that beat in a rhythm to move waste caught in the airways out or to help an ovum (egg cell) travel along the oviducts from the ovaries to the uterus.
The role of villi is to absorb food in the small intestines and water in the large intestine.
Villi are a group of cells that form a structure about 0.5-1 millimetre long.
The walls of the villi are only one cell thick, and there are 10 to 40 villi per square millimetre and number in the millions throughout the small and large intestines.
This vast amount of villi and thin walls increase absorption.
The three types of muscle cells are cardiac (heart), smooth, and skeletal.
Muscle cells contract (shrinking in length) and relax (return to original shape),
helping with movement.
Smooth muscle cells form sheets of muscles. They are throughout the digestive system (amongst other locations), controlling the movement, stiffness, and diameter of the hollow organ they surround.
Skeletal muscles are attached to bones, working with the skeletal system to allow us to move. Through contraction and relaxation, cardiac muscles pump blood around the body, never stopping.
Sperm cells are haploid cells, meaning they have half the amount of chromosomes
and they are the male sex cell.
The middle section of the sperm cell is packed with mitochondria, releasing energy for the flagellum (tail) to move. The goal of a sperm cell is to fertilize an ovum cell
(egg cell).
Roughly 100 million sperm are released to fertilize an egg,
each having an acrosome on the head of the sperm.
The acrosome has enzymes that digest the membrane of the ovum.
Egg cells get fertilised by sperm cells.
They have a haploid nucleus that fuses with a sperm cell’s nucleus to form a zygote cell (fertilised egg cell).
When fertilised, the cell membrane hardens to prevent any more sperm from entering.
The cytoplasm has a large store of nutrients for the embryo’s early development. Egg cells get produced in the ovaries, with one being released each month during the menstrual cycle.
Similar to villi in a human, plants have root hair cells that increase the surface area, increasing the absorption of water and minerals. These root hair cells cover the outside of the roots, holding the plant in place.
A Palisade cell is the main place for photosynthesis to occur. The palisade cell has a higher level of chloroplasts and is found on the top side of leaves. Photosynthesis is the name given to a chemical reaction located inside a chemical called chlorophyll. Chlorophyll is inside the organelle called a chloroplast.
Xylem cells are hollow dead cells that support the plant’s leaves, flowers, and stems as they have a thick cell wall that transports water from the roots to the rest of the plant. Xylem cells transport water in one direction only.
Phloem cells are living cells that transport sugars (and other substances) from the leaves to the rest of the plant.
Phloem cells have a two-way transport system, meaning they can move sugars up or down the phloem.
Phloem cells usually run alongside xylem cells and lose most of their organelles at maturation to be more efficient.
Companion cells are packed full of mitochondria providing energy to the phloem cells (through respiration) for active transport.
Specialised plant cells
Just like animal cells, plant cells have specialised cells that have different roles. Click the cells below to find out more.
From cells to organisms
The hierarchy of multicellular organisms (such as plants and animals) is that different types of cells get organized to keep the organism alive. The levels are cell, tissue, organ, organ system, and organism. Cells (the first tier of this hierarchy)are the smallest unit of life that can live on their own or as a group. Some examples of cells are stem, liver, and collenchyma cells.
Forming tissues
Specialized cells come together to form tissues (second tier) specific to their function. Connective tissue (in animals) binds and supports other tissues. Dermal tissue (in plants) helps prevent water loss.
Forming organs
When a group of tissues comes together towards a collective goal, they form an organ. The liver is an organ (in mammals) that stores glucose produces chemicals, and breaks down other chemicals when required. In a plant, the organs are the leaves, roots, stem, and flowers.
Forming organ systems
When a group of organs (with the same function) comes together, they form an organ system. The two organ systems of a plant are the shoot and roots. The root system is all the organs underground, and the shoot system is all the organs above ground. The respiratory, reproductive, and nervous systems are three of eleven organ systems in a human (Homo sapiens).
Leaf structure
Like humans, plants have essential organs. Leaves are crucial organs for plants. Food production happens in the leaf through photosynthesis.
There are several different shapes and sizes of leaf, and each leaf has adapted for photosynthesis.
Wide leaves can absorb large amounts of sunlight. Thinner leaves can diffuse gas in and out of cells easier.
Red blood cells
Red blood cells are produced in the bone marrow and carry Oxygen around the body. Oxygen enters the lungs diffusing across the alveoli and into red blood cells. Oxygen binds to Haemoglobin located inside the cell to become Oxyheamaglobin. The chemical reaction gets reversed at the required location in the body. To maximize the amount of Oxygen transported by each red blood cell, they don't have a nucleus and increase their surface areas by being biconcave (dips on both sides), allowing Oxygen to diffuse quicker.
Plasma
Plasma is a pale yellow solution consisting of mostly water. Plasma transports glucose, hormones, dissolved salts, enzymes, and the body's waste products. Carbon dioxide (a waste product) gets transported in the plasma back to the lungs. It then diffuses out of the body via the alveoli.
Blood
Blood is a mixture, meaning it has several parts not chemically bound together. The four components are Red blood cells, white blood cells, plasma, and platelets.
In this mixture, red blood cells count for 44% of the volume, plasma is 55%, and platelets and white blood cells combined are just 1%.
Immune cells
The immune system has several components, protecting you from infection and disease. Phagocytes and lymphocytes are two types of white blood cells that are part of the immune system. White blood cells get produced in the bone marrow, and if someone gets an infection, the numbers of white blood cells rapidly increase. Lymphocytes can combine pathogens (bacteria, fungi, and viruses) by producing antibodies. By combining pathogens, Phagocytes are then able to engulf and destroy them.
Platelets
Platelets get made in the bone marrow and can form blood clots or help prevent bleeding by forming scabs. They're small and colourless, and to see platelets stains get used. We model platelets in colour.
The skeletal system
The skeletal system has four roles, support, movement, protection, and the making of blood cells. The femur (thighbone) is the strongest and longest bone in the body, whereas the smallest is the ossicles found in the ear. As an infant, humans have 300 bones that gradually fuse, forming 206 bones by adulthood. Vitamin D and Calcium are needed to maintain strong teeth and bones. Each hand has 27 bones, and a foot has 26.
Movement.
In the skeletal system, joints can move to a variety of degrees. Ligaments and tendons are connective tissues that support the skeletal system by joining bone to bone (ligament) or bone to muscles (tendon), helping the body move.
Support.
Humans can stand upright because the skeletal system supports the muscular system (and the muscular system supports the skeletal system). The human body is born with 300 bones, 33 of which are vertebrae, they allow humans to sit up, and by the time they are an adult, they have 24 as some fuse together.
Producing blood cells.
The production of red blood cells, white blood cells, and platelets occur in the bone marrow of the body's larger bones.
Protection.
The skull (brain), ribcage (lungs, liver, and heart), and vertebrae (spinal cord) all protect the organs inside them.
Hinge joint
Our elbows, knees and ankles contain hinge joints. They allow a back and forth movement. Think of a door opening and closing.
Pivot joint
When we turn our neck, we use a pivot joint. We can also observe the movement of the pivot joint in our forearm. It allows the rotatory movement around an axis.
Ball and socket joint
Our shoulders and hips contain ball and socket joints. It allows a large amount of movement in all directions.
The muscular system
There are three types of muscle cells, cardiac, smooth, and skeletal (all explained in the specialised cells section). Muscle cells join to make muscle tissue, which bundles together to make muscles.
Muscles work in pairs because they can only contract or relax this is called antagonistic muscles. When one muscle contracts, its partner relaxes, pulling the bone forward. The muscles then switch to move the bone back to its original position.
Muscles work with several joints, such as hinge, pivot, and ball and socket.
Stem cells
Stem cells don't have a specialised function and can undergo constant cell division. Humans have embryonic stem cells and adult stem cells. Stem cells can treat diseases and types of cancer but have ethical and social issues associated with using them.
Stem cells, used therapeutically, help to rejuvenate damaged tissue or correct the parts of an organ that aren't working.
Diffusion in cells
Imagine ten people inside a lift. Some people leave the lift, on their floor, and move into a large empty office. The movement of these people is an example of diffusion. They have moved from a highly concentrated space to one with low concentration.
In the same way oxygen, carbon dioxide and glucose move in and out of cells by diffusion. Diffusion happens without the need for energy and only in gases and liquids. This is due to the random movement of their particles.
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