1.1.1 Discuss the Theory That Living Organisms Are Composed of Cells

1.1 Cell Theory

1.1.1 Discuss the theory that living organisms are composed of cells.

All living organisms are composed of cells.

The chemical reactions of a living organism take place within cells.

Cells are formed from other cells.

Cells contain hereditary information and this is passed on from parent cell to daughter cell.

Exceptions to the cell theory:

Muscle fibers consist of multinucleate cytoplasm.(multinucleate cytoplasm: a membrane surrounding cytoplasm with many nucleus, "many cells fused together")

Some fungal hyphae also have multinucleate cytoplasm.

Red blood cells do not have nucleus, no hereditary information.

Unicellular organisms such as amoeba are considered by some biologists to be acellular.

1.1.2 State that a virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat.

Viruses are non-cellular structures consisting of DNA or RNA surrounded by a protein coat.

(Viruses have no metabolism of their own. They only reproduce inside other cells, where they take over the metabolic activities of that cell.)

(Some viruses have a membrane surrounding the protein coat.)

(Some has a few enzymes inside.)

1.1.3 State that cells are formed from other cells.

All cells are formed from other cells by division.

1.1.4 Explain three advantages of using light microscopes(compared to electron microscopes).

Colour images instead of monochrome.(monochrome: black and white)

A larger field of view (approx. 2 mm depending on magnification).

Easily prepared sample material.

Possible to examine living material and observe movement.

1.1.5 Outline the advantages of using electron microscope(compared to light microscopes).

High magnification, sub-cellular structures could be examined.

High resolution, one can see more separate particles and have a clearer view of these particles.

Terms clarified:

Transmission electron microscope: electron passes through specimen.

Scanning electron microscope: electron reflects on the surface of specimen.

Resolution: how close two points can be and still be perceived as two separate points.

Magnification: the ratio of the size of an image to the size of the object.

1.1.4&1.1.5 Compare light microscopes with electron microscopes.

1.1.6 Define organelle.

An organelle is a discrete structure within a cell, and had a specific function. (do not need to be surrounded by a membrane)

1.1.7 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells using appropriate SI units.

Molecules:1 nm

Cell membrane thickness:10 nm

Viruses:100 nm

Bacteria:1 m

Organelles:10 m(mitochondria 0.5 - 5 m, chloroplast 2 - 10 m)

Cells:100 m (10 - 100 m)

Note that cells are three-dimensional shapes.

1.1.8 Calculate linear magnification of drawings.

Magnification = size of image / size of specimen

e.g. size of image: 1 cm, size of specimen: 1m,

magnification = 10 000m /1m = 10000

1.1.9 Explain the importance of the surface area to volume ratio as a factor limiting cell size.

Rate of metabolism of a cell is a function of its mass to volume ratio.

Rate of exchange of materials and energy (heat) is a function of its surface area.

Surface area to volume ratio decreases as size increases.

Larger the cell, higher metabolism, but also smaller surface area, thereby less exchange of materials and heat.

Therefore surface area to volume ratio limits cell size.

1.1.10State that unicellular organisms carry out all functions of life.

Unicellular organisms carry out all the functions of life, e.g. respiration, reproduction, in the only cell.

1.1.11 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.

In multicellular organisms, all the different cells contain the same genes to carry out all different functions.

But only very small part of all the genetic information is expressed in each cell.

Depending on the different genes expressed, each cell carries out specialized functions.

1.1.12 Define tissue, organ and organ system.

Tissue: An integrated group of cells with a similar structure and function. e.g. muscle tissue, blood tissue.

Organ: A group of tissues that carries out a specialized function. e.g. heart

Organ system: A group of organs that carry out a process together. e.g. cardiovascular system

1.2 Prokaryotic Cells (bacteria)

1.2.1 Draw a generalized prokaryotic cell as seen in electron micrographs.

Electron micrograph:

Simplified drawing:

1.2.2 State one function for each of the following: cell wall, plasma membrane, mesosome, cytoplasm, ribosomes and naked DNA.

Cell wall: Protection. Prevents the cell from outside damage and from bursting due to inside pressure.

Plasma membrane: Control of entry and exit of substances.

Mesosome: Infolding of the plasma membrane to increase surface area for respiration.

Cytoplasm: Contains the enzymes for all chemical reactions of metabolism. Also contains naked DNA and ribosomes.

Ribosomes: Main site for protein synthesis.

Nucleoid: The region of the prokaryotic cell that contains naked DNA, one circular DNA molecule. Contains genes which control the cell. (naked DNA: no membrane surrounding, no histones attached.)

1.2.3 State that prokaryotes show a wide range of metabolic activity including fermentation, photosynthesis and nitrogen fixation.

Fermentation: anaerobic conversion to ethanol or lactate. e.g. lactic acid bacteria

Photosynthesis: use light. e.g. cyanobacteria

Nitrogen fixation: convert gaseous N2 to NH3. e.g. nitrogen fixating bacteria.

1.3 Eukaryotic Cells

1.3.1 Draw a diagram to show the ultrastructure of a generalized animal cell as seen in electron micrographs.

Electron micrograph:

Simplified drawing:

1.3.2 State one function of each of these organelles: ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion and nucleus.

Ribosomes: Protein synthesis. Free ribosomes or attached to the rER. Proteins for export are produced at the rER and proteins for intracellular use are produced by free ribosomes.

Rough endoplasmic reticulum: Membrane system with ribosomes attached. Site for protein synthesis. Facilitates transportation of ribosomes from nucleus and produced protein to Golgi apparatus.

Lysosomes: Produced by rER and Golgi apparatus. Digestive enzymes enclosed in a membrane sac. These enzymes are used to destroy non-functioning organelles and invading bacteria.

Golgi apparatus: Receives and modifies products of rER, packs proteins in vesicles for transportation to where needed. Stack of flattened membrane sacks, often with vesicles near by.

Mitochondrion: The site for cell respiration. Releases energy from glucose in form of ATP.

Nucleus: Surrounded by the nuclear envelope. Contains genetic information in the form of DNA (not naked, associated with histones). Controls all the processes in the cell.

(Smooth ER: takes part in lipid production)

(Plasma membrane: Controls what comes into and goes out of the cell.)

1.3.3 Compare prokaryotic and eukaryotic cells.

1.3.4 Describe three differences between plant and animal cells.

1.3.5 State the composition and function of the plant cell wall.

The cell walls in plants provide mechanical support.

The cell wall is made of cellulose.

Cellulose microfibrils form sheets that criss-cross on top of each other to improve strength.

It can be impregnated with other substances such as lignin.

1.4 Membranes

1.4.1 Draw a diagram to show the fluid mosaic model of a biological membrane.

1.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

Phospholipids in the membrane will always have the hydrophilic heads toward both the outside and the inside of the cell with the hydrophobic tails in between.

They are held in place by hydrophobic interaction between the fatty acid tails and hydrogen bonds between the head and H2O molecules surrounding the membrane.

The membranes are fluid, which means that the phospholipids move around, change places but still in the same position.

Cholesterol molecules embedded in the membrane make it less fluid and more stable.

1.4.3 List the functions of membrane proteins including hormone binding sites, enzymes, electron carriers, channels for passive transport and pumps for active transport.

Hormone binding sites (in signal transduction)

Enzymes (catalyze reactions)

Electron carriers (in the electron transport chain during cell respiration or photosynthesis)

Channels for passive transport (facilitated diffusion)

Pumps for active transport (e.g. ATP synthetase)

1.4.4 Define diffusion and osmosis.

Diffusion: the passive movement of particles from a region of higher concentration to a region of lower concentration, as a result of random movement of particles.

Osmosis: Passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (higher water concentration) to a region of higher solute concentration (lower water concentration).

1.4.5 Explain passive transport across membranes in terms of diffusion.

Membranes are partially permeable, allowing small uncharged particles like O2, CO2 to diffuse through without problem.

Larger, polar or ionic substances e.g. glucose, need channels to diffuse through, where the inside of the channel is hydrophilic. This is called facilitated diffusion.

Passive transport such as diffusion, osmosis and facilitated diffusion is driven by the concentration gradient and needs no energy from the cell.

1.4.6 Explain the role of protein pumps and ATP in active transport across membrane.

Active transport moves substances across the membrane against the concentration gradient with the help of a protein pump.

This needs energy which is supplied in the form of ATP.

Particles enter the pump and binds to a specific site.

Energy from ATP is used to change the shape of the pump.

Particle is released in the other side of the membrane.

The pump returns to its original shape waiting for another particle to bind.

1.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.

Proteins are transported inside the cell in vesicles.

Proteins produced by ribosomes on the rER are enclosed in vesicles.

Vesicles fuse with the membrane of the Golgi apparatus, where the proteins are modified and then bud off the Golgi apparatus carrying the modified proteins inside.

The proteins are exported outside the cell by exocytosis, where the membrane of the vesicle fuses with the plasma membrane.

The protein can also remain inside the cell forming a lysosome.

Proteins are transported from in to the cell in vesicles, too.

1.4.8 Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.

Endocytosis is bringing substances inside the cell from outside by folding inwards the plasma membrane and engulfing the extracellular material.

Exocytosis is transporting substances out of the cell by vesicles which fuse with the plasma membrane releasing their contents outside the cell.

The membrane is in a fluid state, which allows it to change shape easily.

If the membrane was not fluid in nature, it would not be able to fuse with vesicles and have vesicles pinch off as in endo- and exocytosis.

1.5 Cell division

1.5.1 State that cell-division cycle involves interphase, mitosis and cytokinesis.

Interphase: The stage of the cell between two successive divisions. It is the largest part of the cell cycle, where the cell is in its “normal life”, e.g. grow in size, and produce proteins etc.

Mitosis: The process in cell division by which the nucleus divides.

Cytokinesis: The division of the cytoplasm of the cell following mitosis. After this, the mother cell is completely divided into two (or more)daughter cells.

1.5.2 State that interphase is an active period in the life of a cell when many biochemical reactions occur, as well as DNA transcription and DNA replication.

1.5.3 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).

1.5.4 Explain how mitosis produces two genetically identical nuclei.

During interphase, DNA replication takes place, forming two identical DNA-replicas due to complementary base pairing.

Mitotic division separates the two identical DNA-replicas to form two genetically identical nuclei.

1.5.5 Outline the differences in mitosis between animal and plant cells.

1.5.6State that cell growth, tissue repair and asexual production involve mitosis.

1.5.7 State that tumors (cancers) are the result of uncontrolled cell division and that these can occur in any organ.

When the control of the cell cycle is lost, the cell will continue to divide even when it is not needed forming a tumor (cancer).

Cancers can occur in any organ (including plants).