Summary Unit 3 - Organisms exchange substances with their environment

Written
by
Mekkie
Kay




TOPIC 3: ORGANISMS EXCHANGE
SUBSTANCES WITH THEIR ENVIRONMENT
A booklet that contains content in the form of questions from real exam papers!




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,Contents (you can use this as a checklist)

MONOMERS AND POLYMERS
□ Monomers and polymers
□ Condensation and hydrolysis reactions

1.2 CARBOHYDRATES
□ Monosaccharides and disaccharides
□ Isomers of glucose
□ Polysaccharides
□ Biochemical tests

1.3 LIPIDS
□ Triglycerides
□ Phospholipids
□ Saturated & unsaturated fatty acids
□ Emulsion test for lipids

1.4.1 PROTEINS: GENERAL PROPERTIES OF PROTEINS
□ Amino acids, dipeptides and polypeptides
□ Structural levels of proteins and the role of bonds
□ Biuret test for proteins

1.4.2 PROTEINS: MANY PROTEINS ARE ENZYMES
□ Introduction to enzymes
Factors affecting rate of enzyme-controlled reactions .

1.5.1 NUCLEIC ACIDS: STRUCTURE OF DNA & RNA
□ Function of DNA & RNA
□ Structure of DNA & RNA nucleotides and polymers.

1.5.2 NUCLEIC ACIDS: DNA REPLICATION .
□ Process of DNA replication
□ Evidence for semi-conservative replication (Meselson and Stahl)

1.6 ATP
□ The structure of adenosine trisphosphate (ATP) ATP/ADP hydrolysis and condensation
□ The properties of ATP make it a suitable immediate source of energy

1.7 WATER




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, □ How hydrogen bonding occurs between water molecules
□ Properties of water that are important in biology

1.8 INORGANIC IONS




RELATIONSHIP BETWEEN THE SIZE OF ORGANISM AND ITS SA:V
- Smaller organisms tend to have a higher SA:V than larger organisms
- E.g. hippo vs. mouse
- This can be calculated and proven mathematically:




RELATIONSHIP BETWEEN SA:V (AND THUS THE SIZE OF AN ORGANISM) AND METABOLIC RATE
- Rate of heat loss / heat lost per unit body mass increases as SA:V increases
- i.e. more heat lost per unit body mass in smaller animals with a high SA:V




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, - So they need a higher metabolic rate / faster respiration
- To generate enough heat to maintain a constant body temperature i.e. replace lost heat


ADAPTATIONS TO FACILITATE EXCHANGE AS THIS RATIO REDUCES IN LARGER ORGANISMS
INCLUDE CHANGES TO BODY SHAPE AND THE DEVELOPMENT OF SYSTEMS
- Larger organisms need a specialised surface / organ for gaseous exchange e.g. lungs
- Because they have a smaller SA:V and a long diffusion pathway (and skin is waterproof / gas tight)
- As well as having a high demand for oxygen and to remove carbon dioxide




ADAPTATIONS OF GAS EXCHANGE SURFACES SHOWN BY GAS EXCHANGE…

Across the body surface of a single-celled organism

- Thin, flat shape
- Large SA(:V)
- Short diffusion pathway/distance (all parts of cell are a small distance away from exchange surfaces)
- For rapid diffusion e.g. oxygen / carbon dioxide


ADAPTATIONS OF GAS EXCHANGE SURFACES SHOWN BY GAS EXCHANGE…

In the tracheal system of an insect

1. Air moves through spiracles (pores) on the surface of the insect
2. Air moves through tracheae
3. Gas exchange at tracheoles directly to/from cells
- Oxygen diffuses down conc. gradient to respiring cell
- Carbon dioxide diffuses down conc. gradient from respiring cells
- Adaptations: lots of thin, branching tracheoles → short diffusion pathway and SA(:V) → rapid diffusion
- Note: rhythmic abdominal movements increase the efficiency of gas exchange by increasing the
amount of air/oxygen entering → maintains greater concentration gradient for diffusion


ADAPTATIONS OF GAS EXCHANGE SURFACES SHOWN BY GAS EXCHANGE…
ACROSS THE GILLS OF FISH


- Counter current flow
- Blood flows through lamellae and water flows over lamellae in opposite directions
- Always a higher concentration of oxygen in water than the blood it is near




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