2 - Basic components of living systems Flashcards
What is a microscope?
instrument that enables you to magnify an object
What do microscopes allow us to discover?
how details of their structure relate to their function
When was the light microscope developed?
16th/17th century
What was the first microscope to be developed?
light microscope
Why could microscopes in the 19th century see individual cells?
had a high enough resolution
What does the cell theory state that both plant and animal tissues are composed of?
cells
What do cells only develop from?
existing cells
How was cell theory developed?
as microscopes had higher magnification/resolution
What is the availability like for light microscopes?
easily available
How expensive is the light microscope?
relatively cheap
What organisms can be observed under a light microscope?
living organisms as well as dead, prepared specimens
How many 2 lenses does a compound light microscope have?
objective and eyepiece lens
Where is the objective lens found on a compound light microscope?
near to the specimen
What is the eyepiece lens?
where specimen is viewed
How does a compound light microscope work?
objective lens produces a magnified image, which is then magnified again by eyepiece lens
What does the objective/eyepiece lens configuration allow for?
- higher magnification
- reduced chromatic aberration
Where is illumination usually provided by in a compound microscope?
light underneath the sample
What is sectioning?
specimens cut into very thin slices with a sharp blade
What is dry mount?
specimen placed on centre of slide and cover slip placed over sample
What are some examples of specimens that can be viewed using dry mount?
hair, pollen, dust (muscle tissue have to be sectioned first)
What is wet mount?
specimens suspended in a liquid e.g. water or immersion oil
How is the cover slip placed on wet mount?
at an angle
What specimens can be viewed using wet mount?
aquatic samples + other living organisms
What are squash slides?
wet mount first prepared, then lens tissue used to press down cover slip
How can potential damage of the cover slip be avoided with squash slides?
squashing sample between two slides
What specimens can be used for squash slides?
soft samples e.g. root tip squashes
What is a smear slide?
edge of slide used to smear sample, creating thin, even coating on another slide. cover slip then placed over
What samples can be used for a smear slide?
blood
How is the sample illuminated in a light microscope?
from below with white light and observed from above
Why do light microscopy images tend to have a low contrast?
most cells don’t absorb a lot of light
What is resolution limited by?
wavelength of light and diffraction of light as it passes through sample
What is diffraction?
bending of light as it passes close to the edge of an object
What is the cytosol of cells?
aqueous interior
What is the cytosols and other cells structures like?
transparent
What do stains do?
increase contrast
Why do stains increase contrast?
different components within cell take up stains to different degrees
What does the increase in contrast allow components to do?
become visible so they can be identified
What is the 1st step for preparing a sample for staining?
placed on slide and air dried
What is the 2nd step for preparing a sample for staining?
heat-fixed by passing through a flame
What is the 3rd step for preparing a sample for staining?
specimen will adhere to the microscope slide and take up stains
What is crystal violet and methylene blue?
positively charged dyes
How does the crystal violet and methylene dyes work?
attracted to negatively charged materials in cytoplasm leading to the staining of cell components
What is nigrosin and congo red dyes?
negatively charged and repelled by negatively charged cytosol
How do nigrosin and congo red dyes work?
stay outside cells, leaving cells unstained, which stand out against stained background (negative stain technique)
What can differential staining do?
distinguish between two types of organisms that would otherwise be hard to identify
What can differential staining also differentiate between?
different organelles of a single organism within a tissue sample
Differential staining: What is the gram stain technique used for?
separate bacteria into two groups, Gram-positive and Gram-negative bacteria
How do you use the Gram stain technique?
crystal violet first applied to bacterial specimen on a slide, then iodine, which fixes the dye. Slide then washed with alcohol
Gram stain technique: What happens when the gram positive bacteria is stained with the crystal violet dye?
retain crystal violet stain and will appear blue or purple under a microscope
Gram stain technique: What happens when the gram negative bacteria is stained with the crystal violet dye?
have thinner cell walls and therefore lose the stain
Gram stain technique: What is the gram negative bacteria then stained with?
safranin dye, called counterstain. these bacteria will then appear red
What is the acid-fast technique used for?
differentiate species of Mycobacterium from other bacteria
What happens in the acid-fast technique?
lipid solvent used to carry carbolfuchsin dye into cells being studied. cells then washed with dilute alcohol solution
What happens to the Mycobacterium during the acid-fast technique?
not affected by the acid-alcohol and retain the carbolfuchsin stain which is bright red
What happens to the other bacteria during the acid-fast technique?
lose stain and exposed to methylene blue stain, which is blue
Pre-prepared slides: What happens during fixing? (1)
chemicals like formaldehyde are used to preserve specimens in as near-natural state as possible
Pre-prepared slides: What happens during sectioning? (2)
specimens dehydrated with alcohols then placed in mould with wax or resin to form hard block. then sliced thinly with knife called microtome
Pre-prepared slides: What happens during staining? (3)
specimens often treated with multiple stains to show different structures
Pre-prepared slides: What happens during mounting? (4)
specimens then secured to microscope slide and cover slip placed on top
What is the function of the nucleus?
It contains genetic information in the form of DNA
What does DNA do?
Directs synthesis of proteins required by the cell
What is the nuclear envelope?
A double membrane that surrounds the nucleus to protect it from damage
How are chromosomes formed?
DNA assosciates with histones to form a complex called chromatin, which then coils and condenses to form chromosomes.
What is the function of the nucleolus?
To produce ribosomes. RNA is used to makes ribosomal RNA, which then combines with proteins to form ribosomes
How do substances enter and leave the nucleus?
Through nuclear pores
How is DNA removed from the nucleus?
It is transcribed to smaller RNA molecules and leaves through the nuclear pores
What is the function of mitochondria?
They are the site of the production of ATP, the final stage of aerobic respiration
What does it mean if there are more mitochondria in a cell?
It would likely be more active
What are the 4 components of mitochondria?
Inner and Outer membrane, cristae, matrix
Why do mitochondria contain a very small amount of DNA?
So they can produce their own enzymes and reproduce themselves
Where are the enzymes used in aerobic respiration found in mitochondria?
The cristae
What is the structure of a vesicle?
A membranous sac (with a single membrane) with fluid inside
What is the function of vesicles?
To store materials and transport them around the cell
What is a lysosome?
A specialised vesicle containing hydrolytic enzymes
What is the function of a lysosome?
They break down waste in cells, including old organelles and pathogens ingested by phagocytes. Also play a role in programmed cell death.
What are centrioles?
A component of the cytoskeleton made up of bundles of microtubules
In what eukaryotic cells are centrioles not found?
Flowering plants and most fungi
What is the function of centrioles?
They are involved in the assembly and organisation of spindle fibres, which separate chromosomes during cell division.
What are the 3 components of the cytoskeleton?
Microtubules, microfilaments and intermediate fibres
What is the structure and function of microfilaments?
They are contractile fibres made up of the protein actin. They are responsible for cell movement and contraction during cytokinesis (the division of cytoplasm during cell division)
What are the functions of the cytoskeleton?
Necessary for the shape and stability of the cell, holds organelles in place, controls the movement of organelles and cell movement.
What is the function of intermediate fibres?
Give mechanical strength to cells and help maintain integrity in the cell.
What is the structure of microtubules?
Polymerised proteins which form tubes.
What are the functions of microtubules?
Act as tracks for the movement of organelles around the cell, form a scaffold-like structure which determines cell shape, make up centrioles.
What is the structure of the Smooth and Rough ER?
A network of membranes enclosing cisternae (flattened sacs). Connected to nuclear membrane.
What is the function of the Smooth ER?
Lipid and carbohydrate synthesis and storage
What is the function of the Rough ER?
Ribosomes bound to its surface make it responsible for the synthesis and transport of proteins.
What do secretory cells have more of than others?
Rough ER and ribosomes bound to it
Where are ribosomes found in the cell?
Either on the Rough ER or free-floating in the cytoplasm
Are ribosomes surrounded by a membrane?
No
What is the structure of a ribosome?
A large and a small sub-unit
What is the function of a ribosome?
It is the site of protein synthesis.
What is the difference between free floating ribosomes and those found on the ER?
Free floating ones tend to produce proteins for use within the cell, whilst ones on the Rough ER tend to produce proteins to be transported out of the cell
What is the structure of the Golgi Apparatus?
Similar to the Smooth ER- compact structure made up of cisternae
What are cisternae?
Flattened sacs
What is the function of the Golgi Apparatus?
Modifies proteins and packages them into vesicles (can be secretory vesicles if the proteins ar leaving the cell or lysosomes)
What are flagella and cilia?
Extensions which produce from some cell types
What are the main differences between flagella and cilia?
Flagella whip-like, longer, cilia hair-like and found in greater numbers
What are the functions of flagella?
Enable some cells’ (i.e sperm cells or prokaryotes) mobility, in some cells act as a sensor detecting chemical changes in the environment
What are the two types of cilia?
Mobile and stationary
What are stationary cilia?
Found on the surface of many cells and provide important function in many sensory organs i.e nose
What do mobile cilia do?
Beat in a rhythmic manner in order to create a current and cause fluids or objects near the cell to move
What are some functions of mobile cilia?
Keeping air passages such as the trachea clear by moving mucus away from the lungs, moving eggs down the fallopian tubes
What is the structure of a cilium (singular cilia)?
Two central microtubules surrounded by 9 microtubules in a wheel-like arrangement (the 9+2 areangement). Parallel microtubules move over each other, causing beating
Where are cellulose cell walls found?
Surrounding the cell surface membrane in plant cells.
How permeable is a cellulose cell wall?
Freely permeable to allow all substances to move
What are the functions of a cellulose cell wall?
Act as a defence against pathogens, give the cell a shape, allow cel, contents to press against it to keep the cell rigid, supports the cell and plant as a whole
What is the structure of a vacuole?
A membrane lined sac containing cell sap
Why do most plant cells have a permanent vacuole?
Important in maintaining rigidity
What Is the membrane of a vacuole called and how permeable is it?
The tonoplast, and it is selectively permeable (allows some small molecules through)
Do animal cells have vacuoles?
Some have a small, non-permanent one
What is the function of a choloroplast?
Site of photosynthesis in plants
Where are chloroplasts found?
The green parts of plants
What are the 7 components of chloroplasts?
- Outer & Inner Membrane 2. Stroma (fluid inside it) 3. Granum (several thylakoids stacked) 4. Lamellae (membranes which join grana 5&6. DNA and ribosomes (used to make own proteins) 7. Starch grains (from photosynthesis)
What do grana contain?
Chlorophyll pigments
What is the advantage of the internal membrane in chloroplasts?
Give a large surface area for photosynthesis?
What is the main difference between prokaryotic and eukaryotic cells?
Prokaryotic cells lack a membrane-bound nucleus and organelles, while eukaryotic cells contain both.
What is the size difference between prokaryotic and eukaryotic cells?
Prokaryotic cells tend to be smaller.
What type of ribosomes are found in prokaryotic and eukaryotic cells?
70s in prokaryotes, 80s in eukaryotes
What 2 things can prokaryotic cells’ cell membranes be made of?
Murein or peptidoglycan
What is the structure of free chromosomal DNA in a prokaryotic cell?
1 molecule of DNA supercoiled, with the genes grouped into operons so some can be turned on or off
What is the difference between flagella in prokaryotic and eukaryotic cells?
Thinner in prokaryotes, energy provided by chemiosmosis rather than aerobic respiration in prokaryotic cells
What is the function of pili?
Used to manoeuvre the cell, can be used for attachment
What does a flagellum contain in prokaryotic cells to help it move?
Microfilaments
What is the purpose of cytosol?
Site of most chemical reactions in a cell
What is the function of free chromosomal DNA?
Contains genetic information, controls cell including which proteins are synthesised
What is the function of the cell surface membrane?
Controls the movement of some substances in and out of the cell
What is the purpose of a plasmid in a prokaryotic cell?
Contains genetic information
What is the function of a slime capsule?
Provides an extra layer of protection for a cell
What is the purpose of a mesosome?
Generates ATP via chemiosmosis
