How the Human Body Works: An Introduction

Light Microscope

Electron Microscope

How they work

A light ray is beamed from a source beneath the specimen and transmitted through the objective and ocular lenses to produce a focused colour image on the retina of the eye when viewed through the eyepiece.

Specimen is mounted in a vacuum and coated in a thin layer of metal to reflect the electrons. In the Transmission Electron Microscope (TEM), an electron beam is transmitted through the specimen and focussed to form a black and white image on a fluorescent screen. In the Scanning Electron Microscope, a fine beam of electrons is scanned onto the surface of the specimen and the electrons scattered by the surface are collected to form a 3D image of the surface, on a fluorescent screen, with poorer resolution than the TEM.

Magnification

Lower magnification, can magnify up to 1,500 x after which image clarity is lost.

Higher magnification, can magnify 500,000 x.

Resolution

Lower resolution- around 200nm.

Higher resolution- around 0.05nm.

Clarity

Lower, due to lower resolution -limited by the wavelength of light.

Higher. The electron beam has a shorter wavelength than light.

Usage

Can be used in educational settings, by hobbyists or in hospitals to observe living processes such as cell division.

Usually found in large laboratories, can only observe dead specimens.

Cost

Relatively inexpensive

Extremely expensive.

Organelle

Function of organelle

Chromatin

Found in the nucleus of the cell and condenses into chromosomes, which carry the DNA when the cell undergoes division. In cells which are not dividing, the Chromatin appears as a diffuse granular mass.

Rough Endoplasmic reticulum

Involved in the manufacture and transport of material to other locations, such as proteins, antibodies and insulin. The rough ER and smooth ER are usually connected. The rough ER has ribosomes attached to the cytoplasmic side of the membrane. It is shaped this way to provide a large surface area for chemical reactions.

Smooth Endoplasmic reticulum

Acts a storage organelle, involved in the production and storage of steroids, lipids and ions. Also has a detoxification function and is a membranous network of folded, smooth tube like sacs – shaped this way to provide a large surface area for the chemical reactions.

Golgi apparatus

Acts as the assembly factory for newly synthesised proteins passing from the channels of the rough endoplasmic reticulum, having carbohydrates added to them, being enveloped and leaving the cell. Composed of flat sacs called Golgi Cisternae, often curved and give it a cuplike shape. Most cells have several Golgi Apparatus and they are more common in cells which secrete protein.

Flagella

A drawn out elongated hair like structure which primarily acts as a method of locomotion in the cells of living organisms. It is long and generates a forward motion by rapidly moving in a wave like pattern and is shaped like this to help it move – such as the tail of a sperm cell.

Mitochondria

Generate the energy the cell needs to do its job. The wall of the mitochondrion consists of two thin membranes, the outer and inner mitochondrial membranes, between them is a small fluid filled space. The inner membrane contains the large central fluid filled matrix and cristae which is a membrane with a series of folds which provides a large surface area for the mitochondria to perform the chemical reactions which are part of aerobic respiration with the synthesis of ATP.

Nucleus

Contains a eukaryotic cell’s hereditary information and controls the cell’s growth and reproduction. A double membrane, the nuclear envelope separates the nucleus from the cytoplasm, both layers of the envelope are lipid bilayers and nuclear pores control the movement of substances between the nucleus and the cytoplasm.

Lysosome

Single membrane enclosed vesicles that form in the Golgi Complex and contain hydrolytic digestive enzymes. Have spherical bodies and carry out digestion within a membrane with which the Lysosomes fuse. Lysosomes can also destroy worn out organelles by fusing with a membrane around the organelles, releasing digestive enzymes and allowing the soluble products to be absorbed back into the cytoplasm. They can also destroy the entire cell when the Lysosome’s membrane will rupture and digest the contents of the cell.

Feature

Diffusion

Osmosis

Active Transport

Use of Energy

Doesn’t require energy and will take place in living and non living systems.

Doesn’t require energy. Water will move from an area of high concentration, to one of low concentration.

Requires energy from respiration. Involves the use of carrier proteins, coupled with ATP which enables them to move molecules against a concentration gradient. Ion gradients created by active transport can then be used to provide energy for the transport of other molecules and ions.

Concentration Gradient

Takes place down the concentration gradient from a region of high concentration, to one of low concentration until equilibrium is reached. Facilitated diffusion will also take place down the concentration gradient, but the diffusing molecule combines with a carrier protein.

Takes place down the concentration gradient until equilibrium is reached. Water molecules can move in both directions across the membrane.

Takes place against the concentration gradient.

Structures that facilitate transport

Cell membrane and a carrier protein is involved in facilitated diffusion.

A selectively permeable membrane.

Uses carrier proteins, coupled with ATP which pump compounds against the concentration gradient.

Molecules transported

Hydrophobic and small uncharged molecules can diffuse through the cell membrane, such as oxygen and carbon dioxide. Large molecules or ions cannot move through the membrane.

Only water molecules are transported via osmosis.

Nutrients and unwanted substances can be transported allowing cells to take in nutrients when the concentration outside is low and vice versa with unwanted substances. For example the sodium-potassium pump in nerve cells which helps nerve impulses.

Type of tissue

How the structure of the tissue is linked to the function

Nerve tissue

Sense stimuli and transmits signals. Allows organism to sense stimuli and respond accordingly. It is comprised of neurons which have a cell body containing the nucleus and other organelles, and projections called Dendrites and Axons. Dendrites are tapering, short cell processes covered in branches called dendritic spines, they are the receiving portion of the neuron and increase the surface area of them to help receive impulses Axons are singular, thin and very long processes which are the output portion of the neuron, conducting nerve impulses to other neurons or other tissues.

Muscle tissue

Consists of muscle fibres that use ATP to generate force. Muscle tissue is classified into three types; Skeletal, Cardiac and Smooth. All have muscle fibres, but structure depends on the location and function. Muscle tissue produces body movements, stabilises body position, produces heat and moves substances and regulates organ volume. Cardiac and smooth muscle is striated and it’s movement involuntary; skeletal muscle tissue movement is usually voluntary. It is specifically adapted to have elasticity, and extensibility; for example in the stomach when expanding to accommodate food and to have contractibility and electrical capability to enable it to perform its functions.

Connective tissue

Widely distributed tissue in the body with a variety of functions depending on location. It binds together, supports and strengthens other tissues, protects and insulates organs, is the transport system of the body and is the storage site of energy reserves and site of immune responses. Consists of cells and extracellular matrix which fills the wide space between the cells. Variations in the composition of the extracellular matrix determines the properties of the connective tissue, for example if it is calcified it can form bone, or teeth. Dense regular connective tissue has loosely packed collagen fibres which are arranged in parallel, and found in ligaments and tendons. This arrangement means they allow some stretch but are resistant to loaded tension forces.

Epithelial tissue

Consists of closely packed continuous sheets of cells, in one or more layers with little intercellular space between them. Lines all major cavities of the body and most organs. There are six types of epithelial tissue but all are separated from the underlying tissue by a basement membrane, which provides structural support and binds it to the neighbouring structures. Depending on the location, the functions of epithelial tissue can include protection, diffusion, excretion and absorption, transportation and movement. Ciliated epithelial cells are columnar and contain goblet cells, they line the upper respiratory tract and move mucus and other substances by ciliary action.