K1/2/1 Cell Biology

Question	Answer
Give an overview of size ranges in biology	Biologists explore life from a microscopic to a global scale: atom - molecule - organelle - cell - tissue - organ - organ system - organism - population - community - ecosystem - biosphere An atom is approximately 0.1nm; a cell is within the range of 1-100μm, their organelles vary in size with the nucleus (5-20μm) being the biggest
State the relationships between the units millimetre, micrometre and nanometre	millimetre (mm); micrometre (μm); nanometre (nm) 1mm = 1000μm 1μm = 1000nm
Define the terms prokaroyte and eukaryote	Prokaryote - a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle Eukaryote - is an organism whose cells have a cell nucleus enclosing the DNA in the shape of chromosomes and other organelles enclosed within membranes
State the three basic principles of evolution	1. Organisms find a niche to survive (e.g. plants close to the ground have larger surface area to height ratio) 2. Organisms develop from simple to complex (e.g. cells did not develop from humans) 3. The strongest offspring survives and therefore traits carried by those are passed on
Explain the term endosymbiosis	Endosymbiosis is a type of symbiosis in which one organism lives inside the other with the two typically behaving as a single organism It is believed to be the means by which organelles such as mitochondria and chloroplasts developed within eukaryotic cells
Explain the endosymbiotic theory	The endosymbiotic theory can be divided into two aspects 1. Primary - a eukaryotic cell engulfs a prokaryotic cell, which then continues to live in the cell in a symbiotic relationship; if one dies the other still survives 2. Secondary - a eukaryotic cell engulfs anohter eukaryotic cell and the two live in a symbiotic relationship; if one dies the other also dies The endosymbiotic theory could be used to explain the development of mitochondria and chloroplasts within eukaryotic cells, as they: are around the same size as bacteria, have their own DNA, reproduce through binary fission like bacteria, have their own double membrane and have their own different ribosomes
State the main differences between an animal and plant cell	Plant cells have a cell wall as well as a cell membrane, while animal cells only have a plasma membrane Plant cells have a large vacuole while animal cells have no or only a small vacuole Plant cells have chloroplasts while animal cells do not Plant cells only have flagella in gametes while they are more common in animal cells
Describe the structure, explain the functions and state the role of the chloroplast	Membrane: a chloroplast has a double membrane, the inner and outer membrane Ultrastructure: the membranes enclose the stroma (the matrix space), which contains disc-like structures called thylakoids, when thykaloids are stacked together it is called a granum (pl. grana); chloroplasts harbor the photosynthetic pigment chlorophyll Function: the site for photosynthesis; participate in several regulatory functions of the cell; photorespiration Role: solar plant for energy supply
Describe the structure, explain the functions and state the role of the nucleus	Membrane: double membrane Ultrastructure: nuclear envelope separates the nucleus from the cytoplasm; the envelope is perforated by nuclear pores and continuous with the ER; contains the nucleolus and chromatin Function: contains most genes and houses chromosomes; the nucleolus makes ribosomal subunits; nuclear pores regulate entry and exit of materials (water, ions and small molecules pass freely through the pores, but flow of larger molecules like proteins or RNA is regulated, thus the pores help control the flow on information); site of transcription of DNA as well as the duplication of DNA before mitosis Role: executive site of the cell
Describe the structure, explain the functions and state the role of the Golgi apparatus	Membrane: single membrane Ultrastructure: flattened membranous cisternae (found in large numbers in secretory cells); contains mainly proteins and material for the synthesis of the cell wall; has a cis (closer to nucleus) and trans (away from nucleus) face Function: concentration; storage and transportation of substances produced in the ER Role: stockroom, central post office
Describe the structure and state the role of the endoplasmic reticulum	Membrane: single membrane Ultrastructure: an extensive network of membranes, ER membrane separates the internal compartment of the ER, the ER lumen, from its surroundings; encloses channel-like fluid-filled spaces called cisternae; it is continuous with the nuclear envelope Role: controlling and regulating trade, forwarding
Differentiate between the two different types of ER and their appearances and functions	The ER can be split into rough and smooth ER (and transitional ER); rough ER has ribosomes on its outer surface while smooth ER does not Smooth ER functions in metabolic processes (e.g. synthesising lipids or steroids) and it produces enzymes that detoxify drugs and poison (especially in liver cells) Rough ER synthesises proteins which are later on secreted
Describe the structure, explain the functions and state the role of the ribosome	Membrane: no membrane Ultrastructure: consists of two subunits containing r-RNA and proteins; are either bound to the surface of the ER or are free ribosomes in the cytoplasm; found in abundance in secretory cells Function: synthesise proteins by the process of translation; site of protein synthesis Role: production facility of produce
Describe the structure, explain the functions and state the role of the mitochondrion	Membrane: double membrane Ultrastructure: two membranes enclose two compartments - between the inner and outer membranes is the first compartment, the second is enclosed within the inner membrane, called the cristae; the cristae's surface area is maximised through invaginations; matrix enclosed within the cristae Function: site of aerobic respiration; production of ATP; has its own DNA and is therefore semi-autonomous Role: intern power plant for energy supply
Describe the structure, explain the functions and state the role of the lysosome, peroxisome, glyoxysome	Membrane: single membrane Ultrastructure: vesicle-like; contains digestive enzymes; can often grow to the size of a mtichondrion Function: break down unnecessary cell material or foreign material (e.g. pathogens); break down hydrogen peroxide Role: recycling plant
Further differentiate between glyoxysomes, lysosomes, peroxisomes and plastids	Glyoxysomes - found in fat-storing tissues of plant seeds; break down fatty acids (some parts can be used in the mitochondria) Lysosomes - contain hydrolytic enzymes that can break down many kinds of biomolecules Peroxisomes - grow by incorporating proteins & lipids from the cytosol (cytoplasm), not directly produced by the endomembrane system; increase in number by dividing when needed, not produced by the ER/Golgi; contains catalase, the enzyme that catalyses the breakdown of H2O2 to H2O (e.g. in breakdown of alcohol or fatty acids) Plastids: plastids are major double-membrane organelles found in the cells of plants, algae, and some other eukaryotic organisms (amongst them are chloroplasts and amyloplasts)
Describe the structure, explain the functions and state the role of the vacuole	Membrane: single membrane Ultrastructure: found in plant and fungal cells as well as in some protists (for water regulation) Function: water regulation; in plant cells - storage of substances (poison, water, irritants, pigments, proteins, minerals), turgor pressure (pressure of water that keeps the plant upright), cell growth; food vacuoles in protists to ingest food Role: storage, warehouse
Name the structures present within a prokaryote and state their functions	Fimbriae - surface appendages that allow a bacterium to stick to a surface Ribosomes - site of protein synthesis Nucleoid region - the cell's DNA, containing genes that control the cell Flagellum - propels the cell, allows the cell to move Capsule - sticky, jellylike protective layer outside the cell wall Cell wall - rigid structure outside plasma membrane which surrounds, supports and protects the cell Plasma membrane - acts as a selective barrier, allows passage of oxygen, nutrients and waste
State the relevance of bacteria	Bacteria are prokaryotes and are very diverse - some are pathogens; some are used for digestion, protection, food production; some are nitrogen-fixing and part of the nitrogen cycle; some are destruents (break down organic material)
Explain why cells are the size they are	cells are generally small in size because of two main reasons - different regions of a cell can communicate with each other rapidly for the cell to function effectively; cells have a large surface area/volume ratio for greater diffusion of substances in and of the cell The larger surface area relative to volume of the cell ensures greater diffusion of - nutrients into the cell, metabolic wastes from the interior to the outside of the cell, respiratory gases i.e. oxygen into the cell and carbon dioxide out of the cell; any damage to the cell can also easily be repaired
Name the three types of microscopy used	Light Microscopy (LM) Transmission Electron Microscopy (TEM) Scanning Electron Microscopy (SEM)
Differentiate between the three types of microscopy	LM - object can be living or dead; specimen either directly examined or stained to make it more visible, vacuum not required; light beam transmitted through a slide, light refracted through glass lenses to magnify the image virtually; max. magnification up to 2,000x; image produced retains natural colour of sample, albeit at a low resolution TEM - object must be dead and in a vacuum; mainly used to study internal ultrastructure of cells, very thin section of specimen used, stained with heavy metals; electron beam transmitted through a slide, electromagnets as lenses to bend electron paths through specimen and to focus them onto a screen to view; max. magnification up to 1,000,000x; produces monochrome 2D images of a high resolution SEM - object must be dead and in a vacuum; especially useful for detailed study of a specimen's surface, specimen coated in thin layer of metal (e.g. gold); electron beam excites secondary electrons on specimen surface that are detected and translated into an image; max. magnification up to 100,000x; produces monochrome 3D image of a high resolution
State the advantages of light and electron microscopy	Light microscopy advantages - fast and easy preparation; images in colour; cheap to purchase; no vacuum needed; mobile and easy to transport; specimen can be living; material is not distorted; Electron microscopy advantages - higher resolution; ultrastructure of a cell visible (TEM); surface of a cell visible (TEM); reveals organelles that are impossible to resolve with light microscopy
Describe the cell wall of plants	The cell wall is a structure that distinguishes the plant cell (present) from the animal cell (not present) and consists of cellulose The wall protects the cell, maintains its shape, prevents excessive uptake of water and holds the plant upright against gravity A young plant cell first secretes a thin and flexible wall, the primary cell wall; between the primary cell walls of adjacent cells is the middle lamella, which glues the cells together; when the cell stops growing and matures, either the primary cell wall is strengthened or a secondary cell wall is added
Describe the extracellular matrix of animals	Animal cells lack a cell wall have instead have an extracellular matrix (ECM), consisting of glycoproteins secreted by the cell; the ECM is attached to the cytoplasmic side of the cellular membrane through integrins By communicating with a cell through integrins, the ECM can regulate a cell's behaviour and coordinate the behaviour of cells within a tissue
Name and explain the different types of intercellular junctions	Plant cells: Plasmodesmata - a channel through the plant cell wall that allows molecules and substances to move back and forth as needed; connects the chemical environment in adjacent cells Animal cells: Tight junctions - tight junctions seal adjacent animal cells in a narrow band to serve a barrier function, prevent leakage and hold cells together Desmosomes - desmosomes are localised patches that hold two cells tightly together, fastening cells together into strong sheets Gap junctions - gap junctions are intercellular channels which permit the free passage between the cells of ions and small molecules; comparable to the plasmodesmata in plant cells
Explain the process of cell fractionation	Cell fractionation is used to isolate (fractionate) cell components based on size and density Cells are homogenised in a blender to break them up; the resulting mixture (cell homogenate) is centrifuged, leading to the fractionation of the components; a series of pellets are formed, overlaid by the remaining homogenate (supernatant); the supernatant is then poured into into another test tube and centrifuged at a different speed and duration; the process is repeated (differential centrifugation) The higher the speed, the smaller the components of the pellet
List the differences between eukaryotes and prokaryotes	Eukaryotes // Prokaryotes Habitat - everywhere // everywhere, including extreme habitats Size - 10-100μm; up to metres // 0.5-2μm Organisation - can be both uni- and multicellular // unicellular Cell wall - cellulose (plants); chitin (fungi) // peptidoglycan Movement - flagella // flagella & fimbriae Cell membrane - present, phospholipid bilayer // present, bilayer, enzymes on cytoplasmic side Nucleus - present // not present DNA - DNA strands (linear) // circular region, nuclear region & DNA Chromosome set - diploid // haploid Cell division - mitosis; meiosis // nuclear fission Plasmids - not present // present Cytoskeleton - present // not present Organelles - present // no organelles except ribosomes
Describe the endomembrane system and explain how it works together	1. DNA is transcribed to RNA, which then becomes mRNA after travelling to the ribosomes before being translated to proteins 2. Proteins are synthesised at the rough ER and a vesicle containing them pinches off headed to the Golgi apparatus 3. The vesicle in the cytoplasm fuses with the Golgi apparatus in which the protein is modified by moving from one Golgi stack to the next in vesicles 4. A vesicle containing the protein buds off the Golgi apparatus and transports it towards its final destinantion (e.g. the membrane, where it is released through exocytosis)
State which cells have a tendency to have more of a certain organelle and why	Macrophages - these cells have many enzyme-filled lysosomes in order to break down foreign bodies Nerve cells & muscle cells - they are very active and need a lot of energy; thus, they have large numbers of mitochondria Pancreatic cells - these cells secrete large amounts of enzymes, which are proteins, so they would need a large number of ribosomes Liver cells - one of the main functions of the liver cell is to detoxify products and thus they need a lot of ER

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	Created by Max Siegel over 6 years ago