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Overview of Cells & Energy (Revision) Essay Sample

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Introduction of TOPIC

Robert Hooke(1665): Published first book on cells. Discovered cells when looking at cork under a microscope. Discovered cell structure of plants.

Anton von Leewenhoek (1650-1700):Dutch. First observed protists. With a simple lens(x200), he observed unicellular organisms & nuclei. By using his ability to grind lenses, he greatly improved the microscope as a scientific tool. He discovered bacteria, protozoa and other small life-forms which he called ‘tiny animals’.

Mattias Schleiden(1838): Deduced theory of ‘photogenesis’ which states that all living things are made of cels or their derivitives.

Theodore Schwann(1839): With Schleiden, Schwann deduced the cell theory- that all animals and plants are made of cells and that within an organism all the cells are identical. Discovered Schwann cells.

Rudolph Virchow (1855): Deduced that all cells are created by other cells. Demonstrated that cell theory applies to diseased tissue as well as living tissue.

Jansen: Invented compound microscope.

Light Microscopes: Light from a source beneath the stage is transmitted through the two lenses in a series, the objective and the ocular (eyepiece) lenses to provide magnifications. Cannot resolve details better than about 0.2 mm(micrometers)

Advantages of light microscopes:

Enables user to see larger structures within eukaryotes and distinguish individual prokyrotes.

They are user-friendly: small, portable, easily-prepared slides, relatively cheap to buy and maintain.

Both living and dead material may be viewed.

Material is rarely distorted by preperation.

Thicker materials may be viewed

Allows experimenter to view image directly.

Allows for specimen to be observed in natural state.

Slides are simple to prepare



Can observe movement.

Electron microscopes: Uses an electron beam instead of a light beam, and electromagnets instead of lenses. Electrons are recorded on a photographic plate, which forms an image on screen.

Advantages or electron microscopes:

Magnifies over 500,000x

Resolving power for biological specimin around 1nm

3-D view instead of one.

Interior view

See organelles than cannot be observed w/ light microscope.

‘Resolution’: Ability to percieve fine detail. Expressed as the minimmum distance between two points for them to be visually distinct. Depends on the lens quality and the wavelength of light used.

‘Magnification: The ratio between the size represented on the microscope and the actual size.

Organelle: A small body inside a cell with a specilised structure that performs a specific function. It also has its own protective membrane.

Relitive Sizes:

1nm: Membrane Thickness

10nm: Viruses

100nm: Bacteria

1-10mm(read’micrometer’): Organelles

less than or equal to 100mm(micrometers): Cells


1 nm: Molecules

10 nm: Cell Membrane

75 nm: Virus

100 nm: Macromolecules

1 mm(micrometer): Bacteria

3 mm: Organelles

10 mm: Cell

Surface area to volume ratio: *The rate of the metabolism of a cell is a function of its mass to volume ratio.* The more active a cell’s metabolism, the more material must be exchanged if the cell is to continue to function. The smaller the cell, the more efficent it is. Larger cells require more energy, but their surface area to volume is closer to one, making them less efficent.

Cell Nucleus: A membrane enclosed organelle containing genetic information.

Possible outdated information:

All living things are made from cells, and all cells are created by other cells.

A virus is a non-cellular structure of DNA or RNA surrounded by a protein coat.

Unicellular organisms carry out all the functions of life

In multicellular organisms, all cells contain genes. By only expressing some of their genes, the cells in multicellular organisms differntiate to carry out specialized jobs.

A tissue is an integrated group oi cells that have a common structure and function.

An organ is a center of the body composed of several different types of tissue and carries out a bodily function.

An organ system is a group of organs the specialize in a certian function together.

1.2 Prokaryotic Cell Structure

Prokaryote: (pro before + karyon kernel) A cell that lacks any membrane bound organelles. Prokaryotes also belong to their own kingdom, bacteria and blue-green algee.

Ribosomes: Small cytoplasmic granules found in all cells. They are smaller than the ribosomes found in eukaryotic cells. They occur singly or in groups called polysomes. They are made of RNA and protein. They are important in protein synthesis. Produces protein for use inside cells.

Mesosomes: Resembles the mitocondria in eukaryotes. They are infoldings of the cell membrane and are important in/site of resperation. Primitive vacoules(deep furrows) to store food or waste.

Slime-Capsule: Surrounds the cell wall of bacteria, it helps to keep the cell from being digested or drying out. Keeps away predatory protazoam white blood cells and bacteriophages.

Flagellum: A small projection from a cell wall that propells a cell. It is an organelle. Flagullum

are accanged around the cell in nine doublets with two single microtubules in the middle. This arrangement is known as the “9+2” pattern.

Cell Wall: Gives the cell it’s shape, protects the cell and prevents the cell from absorbing too much water.

Cell Surface Membrane:Controls the movement of things in and out of the cell. Protects the organellesinside from the outside enviornment. It is made of phospholipids.

Plasmid: An extra-chromosomal, independantly replicating, small, circular DNA molecule. Enables production of antibiotics or resistance to anti-biotics.

Naked Nucleic Acid: Contains the hereditary information of the cell. It regulates protein production.

Cytoplasm: A gelatonus, semi-trasparent fluid that fills most cells.

Cytoskeleton: A structure that maintains the shape of the cell, protects the cell and enables motion, The cytoskeleton plays an important role in inter-cellular transport and cellular division.

1.3 Eukaryotic Cells


ATP: energy molecule used in active transport against the concentration gradient.

Centrioles: vital for reproduction (production of spindle fibres)

Chloroplast: contains chlorophyll and is present only in plant cells. Is involved in photosynthesis.

Concentration gradient: difference of concentration between two substances

Cytolysis: animal cell exploding

Cytoskleteon: maintains in cell shape

Endocytosis: food/liquid going into the cell

Endosymbiosis: The theory that mitochondria and chloroplasts are descended from specialized bacteria. This is because these organelles both contain their own DNA and this DNA is present in a single, continuous molecule, like the DNA of bacteria. Many of the enzymes contained in the cell membranes of bacteria are found in the mitochondrial membranes. Also, they both have their own ribosomes that resemble those of bacteria. Mitochondria can only be produced by mitochondria, like cells from cells. Probably these organelles used to be simple bacteria and were swallowed up by bigger bacteria who could not digest them. In turn these organelles provided the cell with energy in return for protection etc. and turned into an organelle.

Equilibrium: equal amounts moving in and out

Exocytosis: waste going out of the cell

Flaccid: animal cell shrinking

Golgi Apparatus: stacks of flattened membranous sacs. Packages secretions and manufactures lysosomes. Modifies and ‘repacks’ proteins.

Homeostasis: balance

Hypertonic: less water, more solute

Hypotonic: more water, less solute

Isotonic: equal amounts of water and solute

Lysosome: membranous sacs containing hyrolytic enzymes. Hyrolyze proteins and other matierals, including ingested bacteria, and also play a role in cell death by ‘digesting’ the whole cell.

Mitochondrion: (similar to mesosomes in prokaryotes) site of the most of the reactions of cellular respiration; power plants of the cell.

Nucleolus: stores RNA within the nucleus

Nucleus: large spherical structure surrounded by a double nuclear membrane; contains nucleolus and chromosomes. Control center of the cell; contains genetic material. An organelle that stores linear DNA.

Osmosis: movement of H2O in and out of cell

Phagocytsosis: endocytosis of food

Pinocytosis: endocytosis of liquid

Plant cell wall: contains cellulose which is strong tough material. This is important because cells of plants need more structure so that it doesn’t move- the cell wall provides this. It also contains pits and plasmodesmata in the cell wall so that the plant cell can ‘communicate’ with other plant cells.

Plasmolysis: plant cell shrinking

Protein carriers: pumps (active) and channels (passive)

Ribosome: nonmembranous granules composed of RNA and protein- some are attached to ER. Manufacture proteins.

Rough endoplasmic reticulum: network of internal membranes extending through cytoplasm; forms system of tubes and vesicles. Rough sort contains ribosomes which stud the outer surfaces. Manufactures and transports proteins.

Smooth Endoplasmic reticulum: stores proteins, but does not have ribosomes

Turgid: plant cell turning stiff

Turgor pressure: pressure inside the cell

Vacuole: stores excess liquids

Two similarities between prokaryotic and eukaryotic:

both contain a cell membrane, two phospholipid sheets.

both contain the genetic information- that directs a cell’s activities and enables it to reproduce.

Two differences between the eukaryotic nucleus and prokaryotic nuclear material:

in a prokaryotic cell, the genetic material is in the form of a large, circular molecule of DNA, with wihich a vaiety of proteins are loosely associated. This molecule is known as the chromosome. In eukaryotic cells, the DNA is linear, forming a number of distinct chromosomes; morover, it is tightly bound to special proteins known as histones, which are an integral part of the chromosome structure.

Within the eukaryotic cell, the chromosomes are surrounded by a double membrane, the nuclear envelope, but in eukaryotic cells the genetic information is contained within a region called the nucleoid.

Three differences between plant and animal cells:

Plant cells contain a tough, slightly elastic cellulose cell wall in addition to the cell membrane, but this cell wall is a non-living part of the cell. Also, plant cells contain chloroplasts for photosynthesis, animal cells do not.

Animal cells contain centrioles which are involved in cell reproduction, plant cells do not.

Pits and plasmodesmata are found in the cell wall of plant cells, and plant cells also contain a much larger, centralized vacuole.

The Endosymbotics Theory: The endosymbiotic theory assumes that eukaryotes evolved from prokaryotes, because a prokaryotic cell acquired organelles. It states that it is possible that a heterotrophic prokaryote (one which obtains energy and organic matter from inorganic raw materials and an external energy source) which, instead of being digested, became a symbiont (lived in association with) inside the heterotroph, enabling it to carry out photosynthesis. Equipped with its own DNA, the symbiont may be divided inside the host cell very time the host cell itself divided, and in this way the symbiont may have become a chloroplast inside the host cell. Evidence: – Ribosomes in mitochondria and chloroplasts are the same sizes as those found in modern prokaryotes and significantly smaller than those found in the cytosol of a eukaryote. – The inner membranes of mitochondria and chloroplasts have several enzymes and transport systems which resemble those found in the cell membranes of modern prokaryotes. – Mitochondria and chloroplasts have their own DNA in the form of a ring, just as in prokaryotes found today.

Eukaryotic cells have membrane-bound organelles and perform functions in a similar way to organs in an organism.

RER (Rough endoplasmic reticulum)- to isolate and transport proteins which have been synthesised by the ribosomes to other cells. Ribosomes- synthesise proteins

Smooth endoplasmic reticulum- synthesis and transport of lipids and steroids.

Golgi apparatus- assembly point through which raw materials for secretion are funnelled, carbohydrate components are added, and then are shed from the cell.

Lysosomes- destroy unwanted structures (e.g. old mitochondria), or entire cells by the rupturing of the lysosome membrane and the releasing of digestive enzymes (e.g. tadpole tails in frog metamorphosis).

Mitochondria- concerned with the chemical reactions of aerobic respiration; i.e. energy is converted to ATP here (the inner surface is infolded to increase surface area).

Nucleus- contains genetic information (bounded by a nuclear membrane).

Chloroplasts- contain chlorophyll used in photosynthesis

DNA in Prokaryotes Vs. DNA in Eukaryotes:

DNA is loose in prokaryotic cells, in eukaryotic cells the DNA is contained within a nuclear envelope.

DNA in prokaryotic cells is circular, in eukaryotic cells it is arranged in chromosomes

Prokaryotic cells have about 1/1000 as much genetic material.

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