Semester 1: Exam Revision ANSWERS

Unit 1 Biology

Semester 1: Exam Revision ANSWERS

These questions supplement information but are NOT the only ones you need to know. Thoroughly revise notes,questions in your textbook,tests, Biozone and Outcome Tasks. Don’t forget interactive crosswords and podcasts, too.

1. What is the Cell Theory? What tool is used to observe cells? What units are they measured with?

The cell theory is one of the basic principles of biology. The cell theory arose in the mid 1800’s. The cell theory states….

-All living organisms are composed of cells. They may be unicellular or multicellular.

-The cell is the basic unit of life.

-Cells arise from pre-existing cells.

(The cell theory recognises that all living things are composed of one or more cells and that new cells are produced by existing cells)

Microscopes are used to give enlarged images of cells and the structures they contain, and make it possible for us to examine cells with great detail. The unit of measure often used in relation to cell size is the micrometre (µm). 1000µm= 1mm

2. Distinguish between prokaryotic and eukaryotic cells, AND between cytoplasm and cytosolAND between

anabolism and catabolism.

Prokaryotic cells have relatively undefined internal structures and they also lack a clearly defined structure to house their DNA. Organisms that are made up of prokaryotic cells are called prokaryotes and consist of all bacteria and archeans, which are another group of microbes.

Eukaryotic cells have a much more complex structure than prokaryotic cells. All Eukaryotic cells contain many different kinds of membrane bound structures called organelles suspended in the cytosol. These organelles include a nucleus with a clearly defined membrane called a nuclear envelope. The DNA of a eukaryotic cell is located in the nucleus. Organisms made up of eukaryotic cells are called eukaryotes and include all animals, plants, fungi and protists, the single celled organisms. The nucleus of a eukaryotic cell is usually visible with a light microscope, but many organelles in this cell can only be viewed with an electron microscope.

The chloroplast is another organelle that can be easily seen through a light microscope.

Cytosol is the fluid that is inside each living eukaryotic cell that consists primarily of water containing many dissolved substances. (it is not found in prokaryotic cells)

The Cytoplasm is the material surrounding the nucleus of a cell. It consists of a matrix in which the cell’s organelles are suspended. The cytoplasm may be differentiated into the dense outer ectoplasm, which is primarily concerned with cell movement and the less dense endoplasm, which consists of most of the cell’s structures.

3. What is meant by the term partially or differentially permeable in relation tothe cellplasma membrane?

Partially (differentially) permeable describes a boundary that allows only some materials to pass through it.

Plasma membranes of cells are partially permeable as they allow only some dissolved materials to cross it. Due to the presence of a partially permeable membrane surrounding cells, they are able to maintain the internal environment by controlling the movement of substances in and out the cell.

4. Which of the following is an energy-requiring process? - Osmosis, diffusion, active transport, facilitated diffusion

Make sure you know about each of these processes

DIFFUSION (No Energy Required)

- The movement of molecules from an area of high concentration to low concentration. Diffusion stops when both sides are equal or isotonic.(note that by saying that diffusion stops it means that the net movement of molecules into the cell becomes equal to the net movement of molecules out of a cell)

The example below shows diffusion of sugar molecules in water moving from an area of high concentration to low concentration. the high concentration of sugar molecules, over time moves across the semipermeable membrane until the solution on each side is isotonic.

SEMIPERMEABLE MEMBRANE – is a membrane that is selective or only letssomedissolved substances through. It is only partially able to be passed through.

OSMOSIS (No Energy Required)

-A specific ‘type of diffusion’, it is the movement of only WATERacross a semipermeable membrane. The movement of water from a hypertonic solution(higher in concentration) across a semipermeable membrane to a hypotonic solution(lower in concentration) until both sides become isotonic (equal in concentration)

-The net movement of water across a partially permeable membrane without an input of energy and down a concentration gradient. The movement of water from an area of high concentration of water (low concentration of solutes or hypotonic) to an area of low concentration of water (high concentration of solutes or hypertonic)

FACILITATED DIFFUSION (No Energy Required)

-Type of diffusion where the movement of molecules is assisted by carrier proteins. The molecules are still moving from an area of high to low concentration (down a concentration gradient) therefore no energy is needed.Facilitated diffusion is used to move substances that can’t diffuse across the phospholipid bilayer of plasma membranes.

ACTIVE TRANSPORT (Energy Required)

-Movement of molecules in or out of a cell against a concentration gradient of from a low concentration(hypotonic) to a high concentration (hypertonic).

This is not passive movement and requires energy in the form of ATP(adenosine triphosphate) the movement of low to high does not occur naturally therefore it need to physically be moved.

Active transport is the way that plants (usually) get their water + minerals from the soil.

5. Define these terms as they relate to materials crossing a cell membrane: gradient, equilibrium, hypertonic,

hypotonic, endocytosis, exocytosis, phagocytosis, pinocytosis

gradient- The rate of change in growth, metabolism, or physiological activity of a cell or organism.

equilibrium- The condition in which all acting influences are balanced or cancelled by equal opposing forces, resulting in a stable system.

Hypertonic- Having a greater degree of tone or tension.Having a higher osmotic pressure in a fluid relative to another fluid.Pertaining to a solution (e.g. extracelllular fluid) with higher solute concentration compared with another.A solution that has a higher concentration of dissolved substances than the substance to which it is compared.

hypotonic- having a lesser degree of tone or tension, as in a ‘hypotonic muscle’. having a lesser osmotic pressure in a fluid compared to another fluid. refers to a solution with a comparatively lower concentration of solutes compared to another. A solution that has a higher concentration of dissolved substances than the substance to which it is compared.

endocytosis- A process in which cell takes in materials from the outside by engulfing and fusing them with its plasma membrane.

exoctosis- The process in which the cell releases materials to the outside by discharging them as membrane-bounded vesicles passing through the cell membrane.

phagocytosis- The ingestion of bacteria or other material by phagocytes and ameboid protozoans.

A form of endocytosis that involves bulk movement of solid particles into a cell

Pinocytosis- The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.

A form of endocytosis that involves bulk movement of liquids into a cell

6. What is meant by the Surface Area to Volume (SA:V) ratio? Why is it important for a cell to have a high SA:V?

What happens to the SA:V ratio as a cell increases in size? How do some cells or organisms increase their SA?

SA:V ratio is a measure of the number of units of SA available for every unit of internal area

It is important for cells to have a high SA:V ratio to enable them to survive as a high SA:V ratio allows sufficient movement of nutrients into cells however a low SA:V means that the rate of exchange is too slow to allow the cell to receive its required nutrients

The larger the cell, the lower the SA:V ratio due to cells increasing their internal volume faster then their SA increases when the size of a cell increases.

Having really small cells (or whole organisms) enables a high SA:V ratio.

7.Make up a table to summarise the function of these cell structures:cell nucleus, mitochondria, ribosomes,

endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes, chloroplasts, vacuoles, cilia, flagella.

Organelle / Function
Cell nucleus / Contains DNA, it is the control centre of the cell
Mitochondria / Site of energy production in cellular respiration
ribosome / Synthesis of protein
Endoplasmic reticulum / Transports substances within the cell
Golgi apparatus / Stacks of membranes that package materials in vesicles for export
Vesicle / Membrane-bound sac
Lysosome / Site of digestion within a cell
Chloroplast / Site of photosynthesis and storage of starch
Vacuole / Structures filled with fluid (materials + pigments in solution) - large in plant cells
Cilia / (in eukaryotes) whip-like structures involved in cell movement
Flagella / (in bacteria and eukaryotes) whip-like organelle, involved in movement

8. From the human body, list examples of different cells / tissues / organs / systems

This is a very broad question and would most likely take several pages to fully complete, but here are a short list of the basic cells/ tissues/ organs and systems in the human body. They each represent an ascending level of organisation in the body.

Cells (level of organisation 1):Thecellis the basic structural, functional and biological unit of all known livingorganisms.

• Red Blood cells (erythrocytes)
• White Blood cells (leucocytes)
• Stem Cells
• Sex Cells (Ova and sperm)
• Nerve Cells
• Specialised cells for each organ (e.g liver or brain cells)
• Skin cells

Tissues (Level of organisation 2): Any of the distinct types of material of which animals or plants are made, consisting of specialized cells and their products

• Connective Tissue
• Muscle Tissue
• Epithelial Tissue
• Nervous Tissue

Organs (Level of organisation 3): A distinct part of an organism that performs one or more specialized functions.

• Heart
• Liver
• Lungs
• Kidneys
• Brain
• Testicles
• Ovaries

Systems (Level of organisation 4): A group of physiologically or anatomically complementary organs or parts

• Nervous system
• Musculoskeletal system
• Renal System (kidneys)
• Lymphatic System
• Circulatory System

Mixed questions:

a. If you were viewing cells under a microscope, what features could help you determine if they are plant or

animal?

Plant or animal:

Plant cells will have cell walls, while animal cells won’t. SOME Plant cells have chloroplasts (not all cells are photosynthetic) as well and are more rectangular in shape. plant cells usually have large vacuoles

Prokaryote or eukaryote:

Prokaryotic cells don’t have membrane bound organelles therefore they lack a lot of detail. They also lack a nucleus (their DNA is dispersed in their cell). Eukaryotic cells are more complex- they have membrane bound organelles.

b. Is the major site of ATP production the same in a plant cell as in an animal cell? Explain.

• In plants- Chloroplasts and mitochondria- Photosynthesis occurs in chloroplasts but cellular respiration in mitochondria.
• In animals- in mitochondria- Cellular respiration in mitochondria

ATP is produced in the mitochondria in the process of cellular respiration.

(photosynthesis takes place in chloroplasts, the second (light independent) stage of photosynthesis uses C02 + H+ + ATP = C6H1206 + ADP, so if anything ATP is USED in the chloroplasts

c. A scientist wishes to examine ribosomes.Where should they look – in the nucleus or in the cytoplasm?

Ribosomes are found in the cytosol of cells

d. Identify the following as true or false and briefly justify your answers.

i). Plant cells without chloroplasts can capture the energy of the sunlight.
False.
The chloroplast contains a green pigment called chlorophyll which absorbs the light from the sun.

ii). Chloroplasts can be seen through a light microscope.
True.
Chloroplasts are visible under a light microscope, but to discern their specific detail an electron microscope must be used.

e. List at least 2 structures that involved in the process of making protein. What is the contribution of each

organelle to this process?

• Ribosome - Where the synthesis of protein occurs, amino acids join to form proteins
• Nucleus - involved in sending the ribosome (by mRNA) the code for the protein that needs to be made.
• Endoplasmic reticulum - involved in transporting the protein, (rough ER)
• Nucleolus – rRNA production making protein
• Mitochondrion – provides energy for protein synthesis
• Endoplasmic reticulum – series of channels for transport of protein, involved in transporting the protein, (rough ER)
• Golgi body – structure that packages protein for transport out of the cell

f. Name the organelle involved in each of these functions:

Control entry and exit of substances: Cell Membrane
internal transport system: The Endoplasmic Reticulum
energy source of the cell: Mitochondria
‘self destruct button’ for cell: Lysosomes (do not actually make the decision)

Organelles containing a large range of digestiveenzymes used primarily for digestion and removal of excess or worn-out organelles, food particles, and engulfed viruses or bacteria.

site of packaging for export from the cell: The Golgi Complex

9. Why is water so vital for living organisms? What are hydrophilic substances? What are hydrophobic substances?

Water is the most abundant compound in our bodies, it facilitates metabolism,( it is also versatile due to its cohesive nature).

Hydrophilic (polar)- substances that readily dissolve in water

Hydrophobic (non-polar) - substances that tend to be insoluble in water (but can dissolve in fat/ lipids)

• Water is the predominant solvent (a substance in which another substance is dissolved) in all living organisms
• Water molecules are highly cohesive (The intermolecular attraction by which the elements of a body are held together) because of the attraction between hydrogen and oxygen atoms.

10. How do hydrophobic and hydrophilic parts of phospholipids influence the way they form cell membranes?

As the glycerol end of a phospholipid bilayer is hydrophilic while the fatty acid ends are hydrophobic, the glycerol ends tend to go on the outside while 2 layers of fatty acids are formed on the inside, this occurs because cells have fluid outside them (extracellular fluid/ tissue fluid) as well as fluid within them (intracellular fluid/ cytosol) therefore the side that is attracted to water will form the outside layer while the hydrophobic fatty acid ends tend to stay in the inside layer.

• Hydrophilic: Refers to substances that dissolve easily in water; also called polar (outside and inside- blue balls {Glycerol} on diagram below)

• Hydrophobic: refers to substances that tend to be insoluble in water; also called non polar (centre of membrane- Fatty acid tails)

11. What is PHOTOSYNTHESIS? Memorise the balanced equation for photosynthesis. Who does it? Where

does it happen? What in? What is needed for it to happen?

Photosynthesis is a process by which plants tap the radiant energy of sunlight and convert CO2 and H2O into the organic molecule, glucose and at the same time release oxygen.

• BOTH LIGHT ENERGY AND VHLOROPHYLL ARE NEEDED

Plant cells photosynthesise, it happens in photosynthetic cells, it occurs in the chloroplasts of photosynthetic cells. Sunlight, CO2 and water and chloroplasts with chlorophyll are all needed for photosynthesis to occur.

12. Why is CELLULAR RESPIRATION vital for all living things? What are its reactants? What are the products?

Memorisethe balanced equation. What are two difference between aerobic and anaerobic respiration?

Cellular Respiration is vital for all living things as it is the way in which ATP is formed through the release of energy during cellular respiration of glucose. ATP (Adenosine Triphosphate) is required to maintain cellular functions and hence is required to maintain life.

Reactants  Products

Glucose + Oxygen  Carbon Dioxide + Water

C6H12O6 + 6O2  6CO2 + 6H2O

Cell Respiration using Oxygen is termed Aerobic Respiration

Cell Respiration without Oxygen is termed Anaerobic Respiration

Anaerobic Respiration is far less efficient forming only 2 molecules of ATP per 1 Glucose molecule as opposed to Aerobic Respiration creating 36 ATP molecules per 1 Glucose molecule

In humans, a by-product of Anaerobic Respiration is Lactic acid and Carbon Dioxide

(in humans) / Aerobic respiration / Anaerobic respiration
Oxygen or no oxygen / Present / Absent
Number of ATP molecules released / 36- 38 molecules / 2 molecules
End products / CO2 + H2O / CO2 + C3H6O3 (lactic acid)

13. ATP is often described as the energy currency of all cells. How does it store energy for cell functions?

Adenosine triphosphate (ATP) – compound that is the common source of chemical energy for cells and

whose structure comprises one adenosine molecule and three phosphate molecules.

The energy required to maintain cellular functions is in the form of ATP.

ATP is required for….

• Manufacturing chemicals
• New tissue and structure production
• Excretory system
• Digestive system
• Nervous tissue
• Muscle contraction

ATP stores energy in its bonds. ATP releases energy when the third phosphate breaks off and Adenosine triphosphate then becomes adenosine di phosphate (ADP)

• NOTE- In exams you must write Adenosine Triphosphate once with ATP in brackets. For the rest of the exam you can use ATP as long as it was in brackets. This is the same for Adenosine Diphosphate (ADP)
• Adenosine triphosphate (ATP)- then you can just use ATP
• Adenosine diphosphate (ADP)- then you can just use ADP

l. Define autotrophs and heterotrophs.

An autotroph is an organism that uses the process of photosynthesis or chemosynthesis to create its own food. This organism can be a plant or Protist. Some of these organisms includeThe Corpse Lily, Living Rocks and algae. Aheterotroph cannot produce their own food and strive on consuming other organisms to survive. Most common heterotrophs are humans and animals.