Biology - B2

• All living things are made up of cells. The structures of different types of cells are related to there functions.

• To get into or out of cells, dissolved substances have to cross the cell membranes.

Animal and Plant Cells:

Humans and animal cells have the following in common

• A nucleus (Controls the activities of the cell)
• Cytoplasm (Where most chemical reactions happen)
• Cell Membrane (Controls which substances move into and out of the cell)
• Mitochondira (Where most energy is released in respiration)
• Ribosomes (Where protein synthesis occurs)

Plant and Algal Cells:

Plant and algal cells have a cell wall made of cellulose. Cellulose strengthens the cells.

Plant Cells often have:

• Chloroplasts, which absorb light energy to make food
• A permanent vacuole filled with cell sap.

Bacterial Cells

• Bacterial cells consist of a cytoplasm and a membrane surround by a cell wall.
• The genes in a bacterial cells are not in a distinct nucleus.
• Bacterial cells do not have a nucleus

Yeast Cells

• Yeast is a single-celled organism.
• Yeast cells have a nucelus, cytolasm anda membrane surrounded by a cell wall.

Specialised Cells

• Cells may be specialised to carry out a particular function

Dissolved Substances (Diffusion):

• Dissolved substances can move into and out of cells by diffusion.
• Diffusion is the spreading of the particles of a gas, or of any substances in solution.
• Diffusion results in a net movement from a region where they are of a higher concentration to a region with a lower concentration.
• The greater the difference in concentration, the faster the rate of diffusion.

Oxygen required for respiration passes through cell membranes by diffusion.

B2.2.1 - Animal Tissues

• Large multicellular organisms develop systems for exchanging materials.
• As animals develop in the womb, cells differentiate so they can perform different functions.

Tissues:

• A tissue is a group of cells with similar structure and function. Examples of tissues:

- Muscular tissue (Can contract to bring movement)

- Glandular tissue (Produce substances such as enzymes and hormones)

-Epithelial tissue (Covers parts of the body (Skin))

Organs:

• Organs are made of tissues.
• One organ may contain several tissues.

The stomach is an organ that contains:

• Muscular Tissues (Churn the contents)
• Glandular Tissue (Produce digestive juices)
• Epithelial Tissue (Cover the Outside and inside of the stomach)

Organ Systems:

Organ systems are groups of organs that perform a particular function. The digestive system is one example of a system. It has: Glands, The stomach, small intestine, the liver.

Plant Organs:

Plant organs include the stem, roots and leaves.

Examples of plant tissues are:

• epidermal tissues, which cover the plant
• mesophyll, which carries out photosynthesis
• xylem and phloem, which transport substances around the plant

Photosynthesis Equation:

Carbon dioxide + water -> glucose + oxygen

During Photosynthesis:

• Light energy is absorbed by green chlorophyll which is found in some plants and algae.
• The energy is used by converting carbon dioxide and water into sugar
• oxygen is released as a bi-product

Rate of Photosynthesis is limited by:

• Shortage of Light
• Low temperature
• shortage of carbon dioxide

Any of the things above can be a limiting factor

Glucose:

• The glucose produced in photosynthesis may be converted into insoluble starch for storage.
• Plant cells use glucose for respiration

Other uses of Glucose:

• to produce fat or oil for storage
• to produce cellulose (strengthens the cell wall)
• produce proteins

To produce proteins, plant also use nitrate ions that are absorbed from soil

Living organisms form communites. Relationships are formed between communites and these can be affected by external influences.

Distribution of Organisms:

Physical facotrs that may affect the distribution of organisms:

• Temperature
• Availability of nutrients
• Amount of light
• Availability of Water
• Availability of oxygen and Carbon Dioxide

Quantitative data on the distrubtion of oranisms can be obtained by:

• Random sampling with quadrats
• Sampling along a transect

Proteins:

Protein molecules are made up of long chains of amino acids. These long chains are folded to produce a specific shape that enables other molecules to fit into the protein. Proteins act as:

• Structural componenets of tissues such as muscles
• Hormones
• Antibodies
• Catalysts

Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes. Enzymmes are Proteins

Enzymes: 

• The shape of an enzyme is vital for the enzyme's function. High temperatures change the shape.
• Different enzymes work best at different pH values.
• Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in the lining of the gut.
• Amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine.
• Protease is produced by the stomach, pancreas and the small intestine. Protease catalyse the breakdown of proteins into amino acids in the stomach and the samll intestine.
• Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine.
• The stomach produces hydrochloric acid. The enzymes in the stomach work effectively in acid.
• The liver produces bile which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid added in the stomach.

Industrial uses of Enzymes:

Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry.

In the home:

• Biological detergents may contein protein-digesting and fat-digesting enzymes
• Biological enzymes are more effective at love temperatures than other types of detergents.

In Industry:

• Proteases are used to 'pre-digest' the protein in some baby foods
• Carbohydrases are used to convert starch into sugar syrup
• Isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and therefore can be used in slimiming foods.

In industry, enzymes are used to bring about reactions at normal temperatures and pressures that would otherwise require expensive and energy demaning equipment. Enzymes de-nature at high temperatures

Respiration in cells can take place aerobically or anaerobically. The energy released is used in a variety of ways. The human body needs to react to the increased demand for energy during excercise.

Aerobic Respiration:

• The chemical reactions inside cells are controlled by enzymes
• During aerobic respiation (oxygen respiration) chemical reactions occur that: use glucose and oxygen and release energy.
• Aerobic respiration takes place continously in both plants and animals
• Most of the reactions take place inside mitochondria
• Glucose + Oxygen -> CO2 + water (+energy)
• Energy that is released during respiration is used by the organism. The energy may be used:
  • To build larger molecules
  • Enable muscles to contract
  • Maintain a steady body temperature
• During exercise: heart rateand rate and depth of breathing increase.
• Mucles store glucose as glycogen, which can then be converted to glucose during excercise

Anaerobic Respiration:

• During exercise, if insufficent oxygen is reaching the muscles they use anaerobic respiration to obtain energy.
• Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid.
• As the breakdown of glucose is incomplete, much less energy is released than during Aerobic respiration. Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise lactic acid to carbon dioxide and water.
• If muscles are subjected to long periods of vigorous activity they become fatigued, ie. they stop contracting efficiently. Blood flowing through the muscles remove the lactic acid.

Mitosis:

• In body cells the chromosomes are normally found in pairs. Body cells divide by mitosis
• The chromosomes contain the genetic information
• When a body cell divides by mitosis:
  • copies of the genetic material are made
  • then the cell divides once to form two genetically identical body cells.
• Mitosis occurs during growth or to produce replacement cells
• Body cells have two sets of chormosomes; Sex cells (gametes) have only one set
• Cells in reproductive organs - testes and ovaries in humans - divide to form gametes

Meiosis:

• The type of cell division in which a cell divides to form gametes is called Meiosis.
• When a cell divides to form gametes:
  • copies of the genetic information are made
  • Then the cell divides twice to form four gametes, each with a signle set of chromosomes
• When gametes join at fertilisation, a single body cell with new pairs of chromosomes is formed. A new individual then develops by this cell repeatedly dividng by mitosis.
• Most types of animal cells differentiate at an early stage whereas many plant cells retain the ability to differentiate throughout life.
• Cells from human embryos and adult bone marrow, called stem cells, can be made to differentiate into many different types of cells, e.g. nerve cells.
• Human stem cells have the ability to develop into any kind of human cell
• Treatement with stem cells may be able to help conditions such as paralysis
• The cells of the offspring produced by asexual reproduction are produced by mitosis from the parental cells. They contain the same alleles as the parents.

• Sexual reproduction gives rise to variation as gametes fuse and one of each pair of alleles come from a different parent
• In human body cells, one of the 23 pairs of chromosomes carries the genes that determine sex.
  • ** for males
  • XY for females
• Some characteristics are controlled by a single gene. Each gene may have different forms called alleles
• An ellele that controls the development of a characteristic when it is present on only one of the chromosones is a dominant allele
• An allele that controls the development of characteristics only if the dominant allele is not present is a recessive allele
• Chromosones are made up of large molecules of DNA
• A gene is a small section of DNA
• Each gene codes for a particular combination of amino acids whcih make a specific protein.
• Each person (apart from identical twins) have unique DNA. This can be used to identify people

Genetic Disorders:

• Some disorders are inherited
• Polydactyly - having extra fingers and toes - is caused by a dominatnt allele of a gene and can therefore be passed on by 1 parent
• Cystic fibrosis must be inherited from both parents

Embryos can be screened for the alleles that cause these and other gentic disorders.

Old and New Species:

-Evidence for early forms of life comes from fossils

Fossils are remains of organisms from many years ago. They are hard parts of animals

Many early forms of life were soft-bodied so didn't fossilize

We can learn about how species developed through fossils

Extinction:

Extenction may be caused by:

• Changes to the environment
• new predators/more successful predators
• new diseases

New species arise as a result of: Isolation, genetic variation, natural selection and speciation (the populations become so different that successful interbreeding is no longer possible).