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1.1 Studying biology: the practice of science

• Biology - the study of living organisms

• Scientific method is used to design and perform experimental investigations.

  • Well-designed investigations take into consideration current observations and previous results.

The importance of observation

• Observations can reveal how organisms function and how they interact with others + the environment.

  • Observations take advantage of human senses and apparatus for more accurate results.

• They can be interpreted differently based on what one already knows/has experienced.

Learning by experimentation: the scientific method

• Scientists observe what is already known, then ask questions (“why?”); an experimental approach to the study of science.

• Hypothesis- a potential justification/explanation for things that are observed.

  • Can be used to predict events/behaviour.

  • Tested in experiments to determine accuracy; the hypothesis is rejected if inaccurate, supported if accurate.

• Theory - if the hypothesis has been proven as correct under all the conditions that it has been tested in, it becomes this (AKA principle)

Asking the right questions: making hypotheses

• Hypotheses have to be testable, but even if it can’t be tested, it doesn’t mean it’s not correct.

• Gather information that is relevant to proving (or disproving) the hypothesis.

Choosing the right method

• Methods have to be reliable; described in sufficient detail to allow for repetitions of the experiment.

  • If similar results cannot be obtained upon repetition, it is considered unreliable.

  • Avoid personal bias; be objective when collecting and analysing data.

• Results should be clearly stated, separate from discussion of results.

• Multiple trials should be conducted, to prove that results were not because of a one-time fluke.

• Experiments and their results need to be able to replicated in order to be validated.

The need for experimental controls

• Variables that can affect experiment outcomes:

  • Time of day

  • Temperature

  • Amount of light

  • Season

  • Level of noise

• Independent variable - the variable that is being tested. (AKA experimental)

• Dependent variable - the variable that is being measured when the independent variable changes.

• Controlled variable - the variables that are kept constant between experiments

• Control group - a secondary experiment that is identical to the first, bar the single experimental variable being tested.

  • As a controlled experiment, it means that one variable at a time can be tested and its effects can be analysed.

  • Used to eliminate the effects that random factors have on results.

Making valid conclusions

• Valid conclusions depend on reliability of results and their interpretations.

• Speculations - suggestions on what may be occurring based on results.

Conclusion - statement based on the observations and measurements.

Limitations of the scientific method

• Can only be applied to hypotheses that are testable, and to questions that can be answered.

  • e.g it is impossible to conduct experiments around ‘life after death’

• Cannot be used to test moral or ethical issues, but can predict environmental/biological impacts.

1.2 Important principles in biology

• Biological principles - theories that are supported by immense amounts of evidence, that make it unlikely for it to be disproved in the future.

  • Relevant to the way that almost all living organisms function.

• “Organisms are living things”

  Organisms are made of cells

  • Cell theory - a theory which states that all organisms are made of cells, that all cells come from pre-existing cells, and that the cell is the smallest living organisational unit.

  • All cells have a cell membrane that encloses the interior fluid, cytoplasm.

  • All cells have DNA as genetic material.

  Evolution explains diversity

  • Similarities, differences and geographic distribution of organisms → organisms have changed over time.

  • Phylogeny - study of evolutionary relationships between organisms.

  • Scientific classification - hierarchy of names based on phylogenetic relationships that encompasses all organisms.

  Characteristics of organisms

  • Common to all organisms, no matter whether plant, animal, fungi, protist or bacteria.

    • Made of cells

    • Chemically complex and highly organised

    • Exchange energy and matter in their environment

    • Sense and respond to stimuli

    • Grow and reproduce

    • Evolve

  Common requirements for life

  • All life requires a source of energy.

    • Amount of energy depends on organism type, stage of growth, activity level and reproductive state.

  • All life requires nutrients and water for growth, maintenance and repair.

    • Waste is produced as a result of the latter processes.

    • Simplicity of waste excretion depends on size of organism

  • All life is composed of water, organic compounds (proteins, carbs, lipids, vitamins) and minerals.

  • All life requires the ability to sense and respond to stimuli in their internal and external environments.

  Organisms are adapted to their environment

  • Over time, species become adapted to their external environment

  • Natural selection - individuals with features most suited to their environment survive and pass those features down to their offspring.

  • Inherited behaviour and functions make organisms suited for survival in their environment.

1.3 The composition of organisms

• 92 types of naturally occurring elements on Earth (NB. this is approximate and may have changed from the years this textbook was published)

• Organic compounds - complex compounds composed of carbon and hydrogen that are produced or found in living organisms.

• Inorganic compounds - all other compounds that are not formed of carbon and hydrogen.

  • They are still important for living organisms (e.g water, oxygen)

Inorganic compounds

Water

• Most organisms are 70-90% water.

• Chemical reactions that occur in cells happen in a watery medium.

• Water’s properties (such as pH and heat capacity) are very important in biological processes.

• Water molecules are cohesive; strong tendency to stick together.

• Surface tension - Bonds between surface of molecules.

  • Water’s surface tension allows small insects to walk across its surface without ‘breaking’ the molecule.

• Heat capacity - The amount of heat needed to change the temperature of an amount of matter by 1°C.

  • Water’s heat capacity is very high.

  • As chemical reactions occur in the body produce heat, water present in the body can absorb said heat without heating the cells up significantly.

Oxygen and carbon dioxide

• Cellular respiration - the process of releasing energy from food molecules using oxygen.

  • A constant supply of oxygen is needed to keep cells active.

  • Although oxygen can be easily obtained from the atmosphere, solely marine animals are usually small given that oxygen is not soluble in water.

    • Organisms that obtain oxygen from water are small, flat, inactive or have efficient ventilation systems (e.g gills)

• Photosynthesis - the process of making the organic compound glucose with a by-product of oxygen, using carbon dioxide, sunlight and water by plants.

  • Carbon dioxide is converted into energy by plants in photosynthesis, and returned to the environment through organic material decay and as a result of cellular respiration.

  • The “carbon cycle” between organisms and the atmosphere is essential to survival.

Nitrogen

• Nitrogen fixation- the process performed by bacteria of converting atmospheric nitrogen into compounds that plants can be used.

  • Nitrogen is a key component of all proteins and thus is needed in a relatively large amount.

Minerals

• Biologically important minerals:

  • Phosphorous

  • Potassium

  • Calcium

  • Magnesium

  • Iron

  • Sodium

  • Iodine

  • Sulphur

• Mineral ions (mineral salts) are retrieved from weathered rocks and absorbed into plant roots.

  • Also found in cell cytosol, structural components such as bone, and enzyme + mineral molecules.

• Humans require more than 20 different minerals.

Organic molecules

• Four main types:

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acid

• Can be converted from one form to others, in places like the liver.

  • Carbohydrates are converted to fats for storage when food is plentiful.

  • The reverse occurs when food is no longer plentiful.

• Can be linked together into larger molecule chains.

Carbohydrates

• Carbohydrates - compounds made out of carbon, hydrogen and oxygen.

• Most abundant organic compound.

• Important source of energy for organisms.

• Plants - the carbohydrate starch is used to store energy; the carbohydrate cellulose is used to support structure.

• Animals; the carbohydrate glycogen stores energy.

• Monosaccharides - subunits of carbohydrates; simple sugars.

  • Glucose is an example.

  • Monosaccharides have hydrogen/oxygen in the same proportions as water, meaning two hydrogens for every oxygen.

• Disaccharides - two sugars joined together.

  • A molecule of water is removed.

• Polysaccharides- many sugars joined together.

Lipids

• Lipids - fat and oil molecules that store energy.

  • e.g phospholipids (cell membrane component) and steroids (hormones)

• Composed of carbon, hydrogen and vitamins in different proportions to carbohydrates.

  • Smaller proportions of oxygen and can contain other elements (e.g nitrogen).

Proteins

• Thousands of differing types of proteins; functions vary widely.

• Each kind of organisms have own unique proteins.

  • e.g some are hormones, some are carrier molecules.

• All are composed of carbon, hydrogen, oxygen and nitrogen.

  • May also contain sulphur, phosphorus and other elements.

• Composed in chains of units called amino acids.

  • Peptide bonds - the chemical links between amino acids in proteins.

• Proteomics- the study of all proteins in an organism.

Nucleic acids

• Nucleic acids- genetic material of all organisms.

  • Two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acids)

  • DNA contains instructions to assemble new proteins from amino acids.

  • RNA plays a role in protein manufacture.

• Composed of subunits called nucleotides.

Vitamins

• Vitamins - Organic materials used by animals in small amounts.

• Used merely for normal functions.

• Can be naturally synthesised, but other vitamins must be obtained in diet (e.g humans must obtain Vitamin C in our diet because we cannot ‘create’ them ourselves)

• Vitamins can be used to make enzymes.