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THE HUMAN BODY.
1. - THE WAY IN WHICH LIVING THINGS ARE ORGANISED.
The material that forms the living organisms is structured in different
levels:
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Subatomic level: made up of neutrons, protons and electrons.
Atomic level: atoms (the smallest particle that conserves their
properties).
Molecular level: the union of several atoms forms molecules. The
molecules that forms living beings are called bio-molecules. They can
be organic molecules (glucids, lipids, proteins and nucleic acids) or
inorganic molecules (water and mineral salts).
Cells: the building blocks of all living organisms. Cells do not work
alone in living things. They co-operate with other similar cells. Groups
of similar cells combine together to co-operate with each other, as
outline below. There are organisms formed by only a cell (singlecelled organism) and organisms formed by more than one cell
(pluricellular organisms). Pluricellular organisms could have thallus
structure (cells are practically the same and are not specialised in a
concrete function) or tissue organisation (cells of different types, each
type is specialised in an activity).
Tissues: Plants and animals contain many different types of cells.
For example, the cells on the inside of your mouth are very different
from muscular cells or red blood cells. The cells on the outside of a
root of a plant are very different from the green cells in a leaf. Each of
these types of tissue contains cells that are similar in size, colour,
structure and shape and each type also carries out a specific function.
For example, red blood cells carry oxygen. We can define a tissue as
a group of similar cells which carry out the same function.
Organs: Very often several tissues are found working together in a
particular structure in a plant or animal. These structures are called
organs. For example, heart, lungs, liver or flowers are organs. Organs
are the structural and functional units of animals and plants.
Systems and apparatus: Organs which work together form a system
or an apparatus: the eyes, ears, skin, nose and tongue are organs
that join together to form the sensory system.
Organisms: an organism is a living thing, e.g. a human, a dog or a
tree. Each organism is composed of a number of systems and
apparatus that carries out their function together to permit the
organism to work properly and stay alive.
2. - THE CELLS.
In 1665, Robert Hooke used a microscope to look at many living things.
One of the things he looked at was cork, a type of tree bark. He saw that it was
formed by many tiny boxes and he called these them “cells”.
Cells are the unit of life: like bricks that make up a house, cells are the
building blocks that make up all living things. They are very small, so we need
microscopes to see inside them and to examine their structure. There are
organisms, such as bacteria that are unicellular (formed by a single cell). Other
organisms are pluricellular (Formed by millions of cells. Humans have an
estimated 100 trillion or 1014 cells).
We can find basically two kinds of cells: prokaryotic (smaller and without
a nuclear envelope to separate the DNA from the cytoplasm) and eukaryotic
cells (with nuclear membrane). Human cells are eukaryotic. There are two
different kinds of eukaryotic cells: animal and vegetal cells.
The shape and size of cells can vary greatly, depending on the job they
do. Nerve cells, for example, are different from muscle cells, because they do
different jobs. We say that these cells are specialised, because they have
special features for doing their biological functions. Plant cells also show
differences. Respecting to the size, a typical eukaryotic cell size is 10 µm. The
largest known cell is an ostrich egg.
2.1. - STRUCTURE OF HUMAN CELLS.
Human cells are eukaryotic: the nucleus is separated from the rest of the
cell.
Image from http://www.geocities.com/redeagle_pt/imagens/eucariotica.jpg
We can make out three different parts in a eukaryotic cell: the
membrane, the cytoplasm and the nucleus.
2.1.1. - THE CELLULAR MEMBRANE.
The cellular membrane surrounds, protects and separates the cell from
the exterior. It also regulates the transport of substances between the interior
and the exterior of the cell. It is made up by a double layer or lipids. Embedded
within this membrane is a variety of proteins.
Image from www.ncnr.nist.gov/.../biology/cell_membrane.html
2.1.2. - CYTOPLASM
The cytoplasm is the space between the membrane and de nuclear
envelope. It consists of a liquid medium that contains the cellular organelles:
ribosome, mitochondria, vacuole, lysosome, smooth and rough endoplasmic
reticulum, Golgi apparatus, vesicles, cytoskeleton and centrioles. These
organelles carry out the cellular functions.
The cytoskeleton consists of microtubules and microfilaments of
proteins and acts to organize and maintain the cell's shape; anchors organelles
in place and moves parts of the cell.
The ribosomes are made up of proteins and RNA and their function is to
synthesize proteins.
The endoplasmic reticulum (ER) is a set of membranes with form of
saccules and tubes. There are two types, the rough (covered with ribosomes)
and the smooth (without ribosomes). The function of the smooth ER is to make
and transport lipids through the cell, and the rough ER stores and transports the
proteins synthesized by the ribosomes.
The mitochondria are responsible for the cellular respiration, a
metabolic path of the cell to obtain energy.
The Golgi apparatus is a set of flat saccules which store and transport
substances included in vesicles through the cell and to the exterior.
The lysosomes are vesicles that store the digestive enzymes that are
responsible of the cellular digestion.
Vacuoles are saccules of membrane that store different substances.
The centrosome is made of microtubules and is related to the shape
and movement of the cell and its organelles. This organelle is not present in
vegetal cells.
2.1.3. - THE NUCLEUS
The nucleus has spherical shape and is surrounded by a double
membrane: the nuclear envelope, which has nuclear pores to allow the
transport of substances between the nucleus and the cytoplasm.
chromatin
Image modified from www-personal.umich.edu/.../pictures/nulcleus.htm
In the interior we can found the chromatin (Molecules of DNA that carry
the genetic information and are responsible of the regulation of the cell
functions). When the cell is going to divide by mitosis, the chromatin forms the
chromosomes. Other structure present in the nucleus is the nucleoli, which
function is to produce ribosomes.
3. - HUMAN TISSUES.
Multicellular organisms function more efficiently if cells become
specialized for specific functions. A tissue is composed of cells with a similar
structure that function together in a specialized activity.
Image from danus-sebastian.blogspot.com/2007_10_01_archi...
There are four types of tissues found in animals: epithelial, connective,
nerve, and muscle tissue.
3.1. EPITHELIAL
Epithelial tissue is made of closely-packed cells arranged in flat sheets.
Epithelia form the surface of the skin and line cavities and tubes of the body.
The function of this tissue is to cover and protect surfaces. For example, the
epithelium of the skin protects the underlying tissues from mechanical damage,
ultraviolet light, dehydration or invasion by bacteria.
Other type or epithelial tissues is the glandular tissue that forms glands
like the thyroid. Glandular tissue is specialised in secreting substances.
3.2.- MUSCULAR TISSUE
Muscular tissue is responsible for movement. Muscular cells have in their
cytoplasm proteins fibbers of actin and myosin. These fibbers are responsible of
the muscle movement. Three kinds of muscle are found in vertebrates:
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Skeletal muscle is made of long and striated fibbers whose contraction
is rapid and permits the
locomotion and other voluntary body
movements.
Smooth muscle lines the walls of the hollow structures of the body (for
example intestine, urinary bladder, uterus, and blood vessels). Its
contraction is slow and involuntary.
The heart is made of cardiac muscle, made of long and striated fibbers
whose contraction is rapid and involuntary.
3.3. CONNECTING TISSUES
The cells of connective tissue are embedded in a great amount of
extracellular material. This matrix is secreted by the cells that form de tissue
and it consists of protein fibbers surrounded by an amorphous mixture of
protein-polysaccharide molecules. There are five main kinds of connective
tissues:
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Cartilaginous tissue has a support function. Example: the outer ear, the
inter-vertebrae disc, etc.
Bone tissue that forms de bones and has skeletical function. Made of
cells (osteocites) surrounded by matrix. The matrix of bone contains
collagen fibbers and mineral deposits (calcium phosphate, although
magnesium, carbonate, and fluoride ions are also present).
Conjunctive tissues, which join other tissues together, like ligament,
and tendons. Ligaments attach one bone to another and they contain
both collagen and also the protein elastin. Elastin permits ligaments to
be stretched. Tendons connect muscle to bone. The matrix is principally
collagen, and the fibbers are all oriented parallel to each other. Tendons
are strong but not elastic.
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Adipose tissue is fibrous connective tissue in which the cells stored fats
and serves as a thermal insulator and protector. The fat is confined
within membrane-bound droplets. The cells of adipose tissue are called
adipocytes.
Blood tissue. Blood is a very special connecting tissue. It is a liquid
tissue made of cells that float in the plasma.
3.4. NERVE TISSUE
Nerve tissue has the function of detect variations in the external an internal
medium and transmit information and orders from one part to another of the
body. It is composed of nerve cells called neurons and glial cells and forms
the brain, the spinal chord and the nerves.
Neurons are cells specialized in the conduction of nerve impulses. A typical
neuron consists of a cell body which contains the nucleus, a number of short
fibbers (dendrites) extending from the cell body, and a single long fibre, the
axon. The nerve impulse is conducted along the axon.
Glial cells surround neurons. They give support for neurons and there are
various types.
3.5.- SANTIAGO RAMÓN Y CAJAL AND THE NERVOUS TISSUE.
Santiago Ramón y Cajal (1 May 1852 – 17 October 1934) was a
Spanish histologist, physician, pathologist and Nobel laureate. His
investigations of the microscopic structure of the brain were so original that he
is considered by many to be the greatest neuroscientist of all time.
He was born of Aragonese parents in Petilla de Aragón, Navarra. He
attended the medical school of Zaragoza, from which he graduated. After, he
served as a medical officer in the Spanish Army. He took part in an expedition
to Cuba in 1874-75, where he contracted malaria and tuberculosis. In 1883 he
received his Doctor of Medicine degree.
In his investigation, Cajal used a histological staining technique
developed by his contemporary Camillo Golgi. This allowed Cajal to resolve in
detail the structure of individual neurons and led him to conclude that nervous
tissue was composed of individual, autonomous cells, instead of a continuous
web.
4.- HUMAN ORGANS, SYSTEMS AND APPARATUS.
In biology, an organ is a group of tissues that carries out a specific
function. Common human organs are the heart, lungs, brain, pancreas, kidneys,
liver, intestines, skin, etc.
Image from: http://www.williamsclass.com/SeventhScienceWork/CellsOrganization.htm
A group of related organs is an organ system or apparatus. The organs
forming a system are similar while in an apparatus organs are different. Organs
within a system or an apparatus work together to develop more complex
functions. For example the urinary system is comprised of organs that work
together to produce, store, and carry urine. In addition, it is frequent that several
apparatus were implicated in a superior function. For instance, the nervous and
endocrine systems both operate via a shared organ, the hypothalamus, to
coordinate the actions of all the organs, systems and apparatus of the body.
The same is true for the musculoskeletal system, which is responsible of the
movement and of the support of the body. The digestive, urinary, circulatory and
breathing systems are involved in the function of nutrition.
Examples of several human systems and apparatus:
Image from:
http://www.northstar.k12.ak.us/schools/ryn/projects/body/reproductive/markey/webpag
e.html
Image from:
http://commons.wikimedia.org/wiki/File:Female_reproductive_system_lateral.png
Image from:
http://www.cartage.org.lb/en/themes/Sciences/LifeScience/GeneralBiology/Phys
iology/RespiratorySystem/HumanRespiratory/HumanRespiratory.htm
Circulatory system.
Image from:
http://www.williamsclass.com/SeventhScienceWork/CellsOrganization.htm
Image from danus-sebastian.blogspot.com/2007_10_01_archi...
ACTIVITIES:
1.- What are the organs and apparatus responsible for the three vital functions
in living things?
2.- Are all the organs and apparatus of our body related? How?
3.- Complete the table with the next words:
Ligament, sodium, water, erythrocyte, phosphorous, tendon, protein, neuron,
heart, nervous system, skeleton, bone, muscle, blood, eye.
ATOMIC LEVEL
MOLECULAR LEVEL
CELLULAR LEVEL
TISSUE LEVEL
ORGAN LEVEL
SYSTEM AND APPARATUS LEVEL
4.- What mineral salts are for in living beings?
5.- Look for information in internet about prokaryotic and eukaryotic cells. Make
a diagram of these two types of cells and summarize the differences between
them.
6.- Look for information in internet about animal and vegetal cells. Make a
diagram of these two types of cells and summarize the differences between
them. In base of the different structure of both cells, explain why vegetal cells
have autotroph nutrition and why they can not to move.
7.- Explain the difference between thallus and tissue. A fungus, has thallus
structure or tissue structure?
8.- Make a summary about the following terms:
a) cellular organelles
b) tissue
9.- Explain de difference between:
a) mineral salt and lipids
b) prokaryotic and eukaryotic cells
c) organ and system
c) system
bio-molecules
BIBLIOGRAFY:
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Science 3. Biology and Geology. Richmond publishing. (2003). Ed.
Santillana. (Varios autores)
Ciencias de la Naturaleza. Biología y Geología 3 ESO. Proyecto la
casa del saber. (2007). Ed. Santillana. (Varios autores)
Wikipedia, the free encyclopaedia