BIOLOGY UNIT 2: Organisation of living beings

LEVELS OF ORGANISATION OF LIVING BEINGS (NIVELES DE ORGANIZACIÓN DE LOS SERES VIVOS) (What are organisms made of? ¿De qué estamos formados los seres vivos?)

Atoms or Small Macro- Parts elements biomolecules molecules of a Cells Tissues Organs Systems Organism (Elementos (Biomoléculas (Macromolé- cell (Células) (Tejidos) (Órganos) (Aparatos (Individuo) o átomos) Pequeñas) culas) o sistemas)

C H2O Cell H O2 Lípid Membrane Neuron Nervous Mouth Nervous Me O Aminoacid tissue System N Protein Cytoplasm Stomach Cat P Glucose Muscle Muscle Skeletal S Starch Nucleous cell tissue Heart system snail … Organelles

All living things and non-living things are made up of chemical substances (atoms and molecules). The most abundant atoms in living beings are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). These four atoms make up more than 95% of all living matter.

Atoms are linked together to make molecules. The combinations of the atoms C, H, O, N… form molecules of living matter called biomolecules. There are two kinds of biomolecules: inorganic and organic:

- Inorganic biomolecules: they are present in living things and non-living things. Inorganic biomolecules are mineral salts and water. Water is the most abundant substance in all living things (life cannot exist without water).

- Organic biomolecules: they are unique to living things. Organic biomolecules are glucides (example glucose and starch), lipids (example fats and cholesterol), proteins and nucleic acids (DNA and RNA).

Small molecules can join together to form macromolecules, these can join together to form the parts of a cell: cell membrane, nucleus (contains the genetic material) and cytoplasm with organelles, each organelle performs a specific function, for example mitochondrias produce energy, ribosomes synthesize

1 proteins and chloroplasts (only in plant cells) elaborate organic matter through photosynthesis. Exercise: what do all cells have in common?

The cell is the basic structural and functional unit of an organism. Structural because all living beings are made up of one (unicellular organism) or more cells (multicellular organism) and functional because every cell can carry out all the functions of living organisms (interaction, nutrition and reproduction). Exercise: give examples of a human cell performing the 3 vital functions: interaction, nutrition and reproduction.

Tissues are groups of cells of the same type that perform a specific function. Exercise: give the examples of nervous tissue and muscle tissue.

Organs are groups of tissues that perform a specific function. Exercise: is the hand an organ? Explain your answer.

Systems are groups of organs that perform a specific function. Read and repeat the following sentences:

Digestion the digestive system Respiration takes place in the respiratory system Circulation the circulatory system Excretion is carried out by the excretory system Reproduction the reproductive system Movement the muscular and skeletal systems Coordination of all organs and systems the nervous and endocrine systems

2 The defence of our body the immune system PARTS OF A HUMAN CELL

All cells have in common a cell membrane that separates the interior of all cells from the outside environment, a genetic material (DNA) responsible for controlling the cell’s activity and a cytoplasm with organelles. Each organelle performs a specific function. Most organelles are bound by a single or double membrane and a few are non-membrane organelles (ribosomes, cytoskeleton and centrioles). The animal cells (included human cells) have a nucleus that contains the genetic information and the following organelles:

- Ribosomes: they are small non-membranous organelles that are responsible for producing proteins. They are found either moving freely in the cytoplasm or attached to the endoplasmic reticulum. - Mitochondria: these organelles contain a double membrane and are responsible for producing energy through cellular respiration. Cellular respiration is a set of chemical reactions that produce energy using oxygen (we obtain oxygen through the respiratory system) to break down nutrients (carbohydrates, lipids and proteins that we obtain from food through the digestive system). During cellular respiration the energy stored in nutrients is released, but carbon dioxide (CO2) is produced as a waste product (we eliminate CO2 through the respiratory system).

Cellular Respiration: Organic matter + O2 → CO2 + H2O + Energy

3 Exercise: why do we breathe? or why do we die if we stop breathing?

- Endoplasmic reticulum: this organelle is a network of interconnected sacs and channels with a single membrane. It manufactures a variety of substances. There are two types: o Rough endoplasmic reticulum: it has ribosomes attached on its membrane that manufactures proteins. o Smooth endoplasmic reticulum: it does not contain ribosomes and manufactures lipids.

- Golgi apparatus: it receives proteins and lipids (fats) from the endoplasmic reticulum (through transport vesicles). It modifies some of them, concentrates and packs them into vesicles. These vesicles send the substances to different destinations (secretory vesicles) such as the cell membrane or outside of the cell (secretion function).

- Lysosomes: they are vesicles from the Golgi apparatus with a digestive function (they contain digestive enzymes to break down biomolecules).

- Cytoskeleton: this non-membranous organelle is a network of filaments that supports organelles and cell shape and plays a role in cell motion.

4 - Centrioles: these non-membranous organelles direct the movement of the elements of the cytoskeleton. PARTS OF THE NUCLEUS: The nucleus has a double membrane with nuclear pores which are openings that regulate the passage of substances into and out of the nucleus. The genetic information (DNA) is packaged with proteins forming the chromatin that looks like long fibres inside the nucleus. These fibres are condensed into chromosomes when a cell prepares to undergo cell division in order to become two daughter cells. In the nucleus we can see a rounded body called nucleolus that manufactures the ribosomes.

Exercise: identify the following numbered parts of cells.

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CELL SPECIALISATION

All our body cells have the same genetic information (DNA) because all of the cells in our body derive from an initial cell, the cell embryo or zygote (the zygote starts dividing into cells that in turn divide again. After millions of divisions we will have developed a body composed of millions of cells that have the same genetic information as in the zygote). At the beginning the cells that derive from the zygote are stem cells (unspecialised cells) that can be divided and developed into specialised cells with specific functions such as neurons or muscle cells… Differentiation is the process of cells becoming specialised. A group of specialised cells of the same type that perform their specialised function is a tissue. Every tissue has one type of specialised cells and performs its specialised function.

If all our body cells have the same genetic information, why do different specialised cells have different shape and perform different functions? Because each type of specialised cell only uses the genetic information that it needs to perform its specialised function and shape.

TYPES OF TISSUES

All the cells in our body belong to one of the four basic types of tissue: nervous, muscular, epithelial and connective.

NERVOUS TISSUE: The nervous tissue is found in the brain, the spinal cord and the nerves. The neuron is its fundamental cell type. Neurons transmit information using electrical signals called nerve impulses.

MUSCLE TISSUE: This tissue is the predominant component of muscles and enables the movement of our body. The cells are elongated and are called muscular fibres. There are three types of muscle tissue:

- Striated muscle tissue joins bones and contracts voluntarily.

- Cardiac muscle tissue makes up the walls of the heart and contracts involuntarily.

- Smooth muscle tissue moves internal involuntary organs such as the stomach.

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EPITHELIAL TISSUE: This tissue covers all of the internal and external surfaces in our bodies. The cells are tightly connected one to another. There are two types of epithelial tissue:

- Covering epithelium has a protective function. While some are in the form of a single layer of cells (e.g. walls of capillaries, linings of the digestive tract and the trachea), others are several thick cell layers (such as the skin).

- Glandular epithelium: the cells are specialised to produce and secrete particular substances such as hormones, saliva, mucus, tears, sweat, gastric juice… Normally these cells form groups called glands such as salivary glands, sweat glands…

CONNECTIVE TISSUE: This is the most widespread and abundant type of tissue in the human body. The primary role of this tissue is to provide structural support and to hold other tissues in place. Adipose tissue, cartilage tissue and bone tissue are some of the tissues included in connective tissues. Adipose tissue, in addition to serving as a storage site for fats (lipids), also forms an insulating layer under the skin (thermal insulation).

Bone tissue is the strongest type of connective tissue due to the presence of calcium deposits outside the cells. This mineralised tissue is the main component of bones.

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