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Flashcards in Cell Biology Deck (60)
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What are the three laws of Cell Theory

Living organisms are all composed of cells
Cells are the smallest unit of life
All cells come from preexisting cells


What are some exceptions to Cell Theory (3)

Striated Muscle Cell
• Challenges the idea that cells always function as autonomous, independent units
• Much larger than most cells (300mm) and are multi-nucleated (they have multiple nuclei)

Giant Algae
• Challenges the idea that larger organisms are always made of many microscopic cells
• Giant Algae can grow up to 100mm in length, yet are unicellular and contain only one nucleus

Aseptate Fungal Hyphae
• Challenges the idea that living structures are composed of discrete cells
• Aseptate hyphae are not divided up into sub-units because they don’t have septa. Therefore, they have long undivided sections of hypha which will have a continuous cytoplasm with no end wall or membrane and contain many nuclei


What are the 6 functions of life?

Metabolism - living things undertake essential chemical reactions
Reproduction - produce offspring
Sensitivity - respond to internal and external stimuli
Homeostasis - maintenance and regulation of internal cell conditions
Excretion - the removal of waste
Nutrition - synthesis of organic molecules or absorption of organic matter
Growth - increase in size and volume


Outline the functions of life in a paramecium (7)

1. Reactions in the cytoplasm are catalyzed by enzymes
2. Reacts to stimuli: Reveres direction of movement when it touches a solid object
3. Keeps internal conditions within limits
4. Increases in size and dry mass by accumulating organic matter and minerals from its food
5. Expels waste products of metabolism: CO2 from respiration diffuses out of the cell
6. Reproduces asexually or sexually
7. Feeds on smaller organisms by ingesting and digesting them in vesicles


Outline the functions of life in a Chlamydomonas (7)

1. Reactions in the cytoplasm catalyzed by enzymes
2. Reacts to stimuli: Senses where the brightest light is with its eyespot and swims towards it
3. Keeps internal conditions within limits
4. Increases in size and dry mass due to photosynthesis and absorption of minerals
5. Excepts waste products of metabolism: Oxygen from photosynthesis diffuses out of the cell
6. Reproduces asexually or sexually
7. Produces its own food by photosynthesis using a chloroplast that occupies much of the cell


What is the importance of the SA: volume ratio?

1. The surface area affects the rate at which particles can enter and exit the cell while the volume affects the rate at which materials are made or used within the cell
2. As the volume of the cell increases so does the surface area however not to the same extent. As the cell gets larger its surface area to volume ratio gets smaller
3. A cell that becomes too large may not be able to take in essential materials or excrete waste substances quickly enough
4. However, if the cell is too small it might overheat


How can some cells increase their SA? (2)

Special cells can increase their surface area by:
o Changing their shape to be long and thin
o Halving folds in the cell membrane


Why do cells reproduce? (3)

o For growth in multicellular organisms
o For reproduction in single-cell organisms
o To replace dead/damaged cells


What are emergent properties?

Emergent properties are properties of a group that are not possible when any of the individual elements of that group act alone. (cells-> tissues - > organs)


What are stem cells?

Cells with the potential to develop into many different types of specialized cells in the body


How do stem cells differ from other cells? (2)

o Self-Renewal: Stem cells can continually divide (self-sustaining)
o Potency: Stem cells are undifferentiated (unspecialized) and can differentiate in different ways to produce different cell types


Outline the role of stem cells in embryonic development (6)

1. After fertilization, a zygote is formed in all multicellular organisms
2. After the formation of a zygote, there is a large increase in the number of cells. This relies on the ability of stem cells to continually divide
3. Early embryonic stem cells are capable of becoming any type of specialized cell (pluripotent stem cells)
4. Subsequently, cells of the embryo start to commit to different pathways of cell differentiation and become limited in the types of specialized cells they can form
5. Embryonic development results in a unique body pattern with organs and tissues comprising of specialized cells
6. Fully specialized cells are no longer flexible to form other types of specialized cells


Where can stem cells be found? (3)

• Embryonic stem cells: Cells from the embryo that are undifferentiated can become any time of cell. These are found in the inner cell mass of blastocysts
• Adult stem cells: Cells found in certain adult tissues that can become a limited number of types of cell. Adult tissues include the bone marrow or liver
• Blastocysts are a thin-walled hollowed structure in early embryonic development that contains a cluster of cells called the inner cell mass from which the embryo arises)


Outline two therapeutic uses of stem cells

Stargardt’s Disease
• Stargardt’s disease: A genetic disease that can cause blindness in children
• Stargardt’s disease affects a membrane protein in the retina causing photoreceptor cells in the retina to become degenerative
• Stargardt’s disease is treated by injecting embryonic stem cells that can develop into retina cells into the back of the eyeball

Parkinson’s Diseases
• Parkinson’s disease: A degenerative disorder of the central nervous system caused by the gradual loss of dopamine-producing cells in the brain
• Dopamine is a neurotransmitter responsible for transmitting signals involved in the production of smooth, purposeful movements. Those with Parkinson’s disease typically exhibit tremors, rigidity, slowness of movement and postural instability
• Parkinson’s Disease is treated by replacing dead nerve cells with living, dopamine-producing ones


Outline the main ethical concerns regarding stem cells

o The health and quality of life of patients suffering from otherwise incurable conditions may be greatly improved
o Early stage embryos lack a nervous system so do not feel pain or suffer in other ways during stem cell procedures
o If embryos are produced deliberately, no individual that would otherwise have had the chance of living is denied the chance of life
o Larger numbers of embryos by IVF are never implanted and do not get the chance of life

The use of stem cells involves the creation and death of an embryo that has not yet differentiated in order to obtain embryonic stem cells. Thus, is it ethically acceptable to create a human embryo even if it could save human lives?


Outline the structure of prokaryotes (6)

• Prokaryotes are unicellular organisms that lack membrane-bound structure
• Hence, prokaryotes do not have a nucleus and instead generally have a single chromosome
• Prokaryotic chromosomes have a single, circular double stranded DNA located in an area of the cell called the nucleoid
• Most prokaryotes have a cell wall outside the plasma membrane
• Two of the three major domains are prokaryotes: Bacteria and Archean
• Prokaryotes are also small (between 1-10μm)


Outline the structure of eukaryotes (4)

• Eukaryotes have membrane bound organelles despite having a cytoplasm like prokaryotes
• Furthermore, eukaryotes compartmentalized their organelles.
• Eukaryotic cells are larger (5-100μm) than prokaryotic cells
• Eukaryotes consist of both animal and plant cells:


What are the advantages of compartmentalization? (4)

Compartmentalization allows for different chemical reactions to be separated from other organelles and allows for an increase in efficiency
o Efficiency of metabolism: Enzymes and substrates can become localized and much more concentrated
o Localized conditions: Different pH and other factors can be kept at optimal levels
o Toxic/damaging substances can be isolated: E.g. digestive enzymes can be isolated
o Numbers of organelles can be changed depending on the cell’s requirements


Outline the process of binary fission (3)

• For unicellular organisms, cell division is the only method used to produce new individuals. Prokaryotes reproduce asexually using the process of binary fission
1. The chromosome is replicated and each identical copy is moved to either end of the cell
2. The cell elongates. New cell wall forms and plasma membrane pinches in
3. Cross walls form two separate cells. The two new cells separate


Plants Vs Animal Cell (7)

Cell wall
Chloroplasts present
Large central vacuole
Store excess glucose as starch
No centrioles within the centrosome area
Generally have a fixed regular shape
Do not have cholesterol in cell membrane

No cell wall
No chloroplasts
Vacuoles absent or small
Stores excess glucose as glycogen
Has centrioles within the centrosome area
Generally have an amorphous (flexible) shape
Have cholesterol in membrane


Prokaryote vs Eukaryote

DNA in a loop form, with no proteins
DNA free in the cytoplasm
No membrane-bound organelles
70s ribosomes
Size less than 10μm

DNA wrapped around proteins
DNA enclosed within nucleus
Has membrane-bound organelles
80s ribosomes
Size more than 10μm


Light Microscope vs Electron microscope

Light microscope
Light rays
Living or dead can be viewed
Small & portable
Easy to use
Relatively cheap

Electron microscope
Electron beams
x500 000
Has to be dead
Time consuming to set up
Very expensive


What is resolution?

Resolution: The shortest distance between two points that can be distinguished


List the organelles within prokaryotes (8)

Plasma membrane - allows certain substances through and in charge of homeostasis
Cell Wall - provides the cell with a strong shape and makes it rigid
Nucleoid - stores genes and site of DNA replication
Ribosome - synthesises proteins
Cytoplasm - jelly like fluid where chemical reactions take place
Pili - enable adhesion to substances and sexual conjugation
Flagella - allows cell movement
Plasmid - aids DNA exchange


List the organelles with eukaryotes (6)

Vacuoles - contains cell sap and used for storage of water to increase cell turgor
Mitochondria - provides the cell with ATP energy
Lysosomes - Membrane-bound vesicles that contain enzymes for intracellular digestion. It is important for cell defence, digesting harmful organisms and chemicals.
Smooth/Rough Endoplasmic Reticulum - folded membranes that modify proteins
Cell membrane - lipid bilayer that acts as a protective barrier
Golgi Apparatus - marks and secretes proteins


What is a phospholipid? (3)

• Phospholipids: A lipid consisting of a glycerol, bound to two fatty acids and a phosphate group
• Phospholipids are made up of two parts, a phosphate head and a fatty acid tail
• Lipids are amphipathic as:
o The head is hydrophilic (water-loving) and is attracted to water
o The tail is hydrophobic (water-hating) and is repelled by water


Describe the characteristics of a membrane (4)

• Characteristic of membranes include:
o Flexible: Move and form a variety of shapes
o Strong: The hydrophobic region hates water so much that the repelling nature keeps the membrane together
o Self-healing: A hole in the membrane will self-heal due to the hydrophobic region’s hatred of water
o Semipermeable: Only some solutes may pass through the membrane


What is the difference between integral and peripheral proteins?

o Integral proteins: Permanently embedded
o Peripheral proteins: Temporary embedded


What are the functions of proteins in the membrane? (J.E.T.R.A.T)

o Junctions: Connects cells together
o Enzymes: Can act as enzymes
o Transport: Responsible for facilitated diffusion and protein pumps
o Recognition: For cells to identify each other
o Anchorage: Attachment points for the cytoskeleton
o Transduction: Receptors for hormones


What is the role of cholesterol in membranes (3)

• Membranes need to be fluid enough so the cell can move and necessary substances can move across the membrane
• However, if too fluid the membrane could not effectively restrict the movement of certain substances across itself
• Cholesterol controls membrane fluidity by making the phospholipids pack more tightly and regulates the fluidity and flexibility of the membrane by preventing tails from touching and crystallizing the membrane