Chapter 2 - Basic components of living organisms Flashcards
Cell surface membrane
- Physical barrier
- Controls what moves in and out the cell
- Enables cell to communicate with surroundings
- formed from phospholipid bilayer - diameter of 10nm
- partially permeable
- all cells
Cell wall
- Made of peptidoglycan (murein) in bacterial cells and cellulose in plants
- Provides strength and rigidity
- Narrow threads of cytoplasm called plasmodesmata connect the cytoplasm of neighbouring plant cells
- freely permeable
- plant cells NOT animal
Nucleus
- double membrane = has pores
- contains chromatin
↳ chromosomes are made of sections
of linear DNA tightly wound around
proteins called histones - DNA stored replicated and copied into messenger RNA
- all eukaryotic EXCEPT RBC
- -> via transcription
Mitochondria
- aerobic resp within ALL eukaryotic cells
- Surrounded by double membrane = inner membrane folded to form cristae
- matrix formed by cristae contains enzymes needed for aerobic resp
- small circular pieces of DNA and ribosomes found in matrix
- Rod shaped
- In cytoplasm
Chloroplasts
- larger than mitochondria
- membrane bound compartments called thylakoids containing chlorophyll stack to form grana
- grana joined together by lamellae
- light-dependent stage takes place in the thylakoids
- light-independent stage (Calvin Cycle) takes place in the stroma
- plant cells
Ribosomes
- freely in cytoplasm or as part of RER
- complex of ribosomal RNA (rRNA)
- 80S (60S small and 40S large subunits) in eukaryotic
- 70S (30S small and 50S large subunits) in prokaryotes, mitochondria and chloroplasts
- site of translation
- all cells
- Involved in process of translation, proteins synthesised from mRNA
Endoplasmic reticulum
ROUGH ER:
- studded with ribosomes, site where proteins are made folded and moved to golgi
- formed from continuous folds of membrane continuous with the nuclear envelope
- Plant and animal cells
SMOOTH ER
- lipid and steroid synthesis and drug detoxification
- plant and animal cells
Golgi apparatus
- flattened sacs of membrane similar to SER
- Modifies packages and directs newly made proteins & lipids into golgi vesicles
- vesicles transport to destination
- plant and animal cells
Large permanent vacuoles
- sac in plant cells surrounded by tonoplast, selectively permeable membrane
- vacuoles in animal cells are not permanent and small
Vesicles
- found in plant and animal cells
- membrane-bound sac for transport and storage
Lysosomes
- specialist form of vesicles
- Contains hydrolytic enzymes (to break down waste materials such as worn out organelles)
- used by cells in immune system and in apoptosis
Centrioles
- Hollow fibres made of microtubules
- Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
- Not found in flowering plants and fungi
- Organises microtubules into spindles on which chromosomes are separated when cell divides
Microtubules
- Makes up the cytoskeleton of the cell about 25 nm in diameter
- Made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments - 13 protofilaments in a cylinder make a microtubule
- Moves organelles and cytoplasm using molecular motors
- all eukaryotic cells
Microvilli
- cell membrane projections
- increase SA to increase rate of exchange of substances
- specialised animal cells
Cilia
- Hair-like projections made from microtubules
- Allows the movement of substances over the cell surface
- push mucus towards stomach
Flagella
- Rigid whip like tails that contract to move
- Prokaryotes —> made from flagellin protein
- Eukaryotes —> made from tubulin and surrounded by cell membrane
- specialised cells
The importance of the cytoskeleton
- strength and support = mechanical strength = provides scaffolding to maintain shape of cell
- supports the organelles, keeping them in position
- cytoskeleton aids transport within cells by forming ‘tracks’ along which organelles can move (endocytosis & exocytosis)
- enables cell movement via cilia and flagella
Plasmids
- small loops of DNA, separate to main circular DNA molecule
- contain genes that can be passed between prokaryotes (in antibiotic resistance)
Slime Capsule
- Outermost layer of the prokaryotic cell (like bacteria)
- protects bacteria from drying out and attacked by immune system cells
Microfilaments
- Made from repeating actin subunits
- Responsible for Cell movement
&
Change in shape
&
Muscle contraction - Thinnest component of cytoskeleton
Pili
- Appendages –> smaller than flagella
- for attachment to other cells or surfaces in sexual reproduction
- can ‘fix’ the cell to a surface and can aid the exchange of genetic info between cells like bacteria
Extracellular Matrix
- Material between cells that hold tissue together
- Made: scaffolding proteins e.g collagen
- Important for cell to cell signalling
Nucleoid region
- Region of the cytoplasm containing circular DNA
- Viewed by e- microscope
Optical Microscopes
➜ light limits resolution
➜ max res = 0.2 µm (micrometres )
➜ max mag = x1500
Good:
- cheap
- easy to use for schools
- portable
- study live specimen
Bad:
- magnification weak compared to e- microscope
Laser scanning microscope (confocal microscope)
➜ cells being viewed must be stained with fluorescent dyes
➜ Multiple depths of the tissue section/organisms are scanned to produce an image
Good:
- high resolution and contrast
- can focus on structures at different depths within specimen
- can be used on thick or 3D specimen
Bad:
- slow process
- laser can cause photodamage to cells
Electron microscope
- uses fast travelling e-
- great resolution (0.0002 µm or 0.2 nm)
➜ max mag = x1,500,000 - e- fired from cathode and focused by e- magnets on to screen/photographic plate
- 2 types SEM and TEM
- image produced: micrograph
- specimen has to be chemically fixed by being dehydrated and stained
Electron microscope - SEM
Good:
- 3D image
- artificial colour can be added via computer tech
- can be used on thick or 3D specimens
- magnification of 500,000 +
Bad:
- black and white image
- Lower res than TEM
- specimen must be kept in vacuum - no live
- specimen must be coated in metal film
Electron microscope - TEM
Good:
- magnification from 500,000 to 2 million
- potential new ones going to 50 million
- resolution very good
- can see internal structures
Bad:
- 2D imaging only
- black and white image
- specimen must be kept in vacuum and dead and very thin
- tedious and large and bulky
- temp control
- expensive and technical training required to handle
Optical slide production 1
1.) FIXING
↳ ꜰᴏʀᴍᴀʟᴅᴇʜʏᴅᴇ ᴛᴏ = ʀᴇᴛᴀɪɴꜱ ɴᴇᴜʀᴀʟ ꜱᴛᴀᴛᴇ
2.) SECTIONING
↳ ᴅᴇʜʏᴅʀᴀᴛᴇᴅ ᴡɪᴛʜ ᴀʟᴄᴏʜᴏʟ, ɪᴍᴘʀᴇɢɴᴀᴛɪɴɢ ɪᴛ ɪɴ ᴘᴀʀᴀꜰꜰɪɴ/ʀᴇꜱɪɴ ꜰᴏʀ ꜱᴜᴘᴘᴏʀᴛ, ᴘʟᴀᴄᴇᴅ ɪɴ ᴡᴀx ᴍᴏᴜʟᴅ ᴀɴᴅ ꜱʟɪᴄᴇᴅ ᴡɪᴛʜ ᴍɪᴄʀᴏᴛᴏᴍᴇ
3.) STAINING
↳ ᴘᴀʀᴀꜰꜰɪɴ ʀᴇᴍᴏᴠᴇᴅ ᴀɴᴅ ɢʀᴀᴍ ꜱᴛᴀɪɴɪɴɢ ᴏʀ ᴀᴄɪᴅ ꜰᴀꜱᴛ
4.) MOUNTING
↳ ꜱᴇᴄᴜʀᴇ ᴛᴏ ꜱʟɪᴅᴇ ᴜꜱɪɴɢ ʀᴇꜱɪɴ ᴀɴᴅ ᴄᴏᴠᴇʀꜱʟɪᴘ ᴏɴ
Optical slide production 2
∘ ꜰʀᴇᴇᴢᴇ ᴛʜᴇ ꜱᴘᴇᴄɪᴍᴇɴ ɪɴ ᴄᴀʀʙᴏɴ ᴅɪᴏxɪᴅᴇ ᴏʀ ʟɪQᴜɪᴅ ɴɪᴛʀᴏɢᴇɴ
∘ ᴄᴜᴛ ᴛʜᴇ ꜱᴘᴇᴄɪᴍᴇɴ ɪɴᴛᴏ ᴛʜɪɴ ꜱʟɪᴄᴇꜱ ᴜꜱɪɴɢ ᴀ ᴄʀʏᴏꜱᴛᴀᴛ
∘ ᴘʟᴀᴄᴇ ᴛʜᴇ ꜱᴘᴇᴄɪᴍᴇɴ ᴏɴ ᴛʜᴇ ꜱʟɪᴅᴇ ᴀɴᴅ ᴀᴅᴅ ᴀ ꜱᴛᴀɪɴ
∘ ɢᴇɴᴛʟʏ ᴘʟᴀᴄᴇ ᴀ ᴄᴏᴠᴇʀꜱʟɪᴘ ᴏɴ ᴛᴏᴘ ᴀɴᴅ ᴘʀᴇꜱꜱ ᴅᴏᴡɴ ᴛᴏ ʀᴇᴍᴏᴠᴇ ᴀɴʏ ᴀɪʀ ʙᴜʙʙʟᴇꜱ
Gram staining
Positive:
- crystal violet followed by iodine
- washed with alcohol
- gram positive = retains dye
- purple under microscope
Negative:
- lose dye
- stained with safranin dye (counterstain)
- appears red/pink
Acid fast
- Differentiates species of mycobacterium
- lipid solvent = carries carbolfuschin dye
- washed with dilute alcoholic solution
- mycobacterium are not affected by the acid alcohol and retain the bright red dye
- other bacteria lose stain and then stained with methylene blue
Types of slides
Dry mount
- hair, pollen
Wet mount
- aquatic samples, living organisms
- add drop of water/immersion oil
Squash slides
- soft samples e.g root tip squash
Smear slides
- A drop of blood and use slide to smear
CELL THEORY
- BOTH plant and animal tissue is composed of cells
- Cells are the basic unit of life
Cells only develop from existing cells
Magnification = Eyepiece magnification × objective magnification
Magnification = (Image size)/(object or actual size)
Magnification
how many times bigger the image of a specimen observed is in compared to the actual size of the specimen
Resolution
the ability to distinguish between two separate points
