Cell structure

cell

smallest unit of a living thing

who founded the term cells and when

robert hooke in 1665

what’s the formula for magnification

magnification = image size/actual size

what’s magnification

how many times larger the image is than the actual object.

what’s resolution

the minimum distance between two points that can still be distinguished as separate

how does a smaller distance affect the resolution

the smaller the distance the higher the resolution

how do you convert mm to µm

times by 1000

how do you convert from mm to nm

times by 1000000

how do you convert from µm to cm

divide by 10000

how do you convert from nm to µm

divide by 1000

which part of a microscope has a graticule

eyepiece

what equipment is used to calibrate a graticule

stage micrometer

what’s another name for a light microscope

optical microscope

what type of image is produced by a light microscope

2D colour image

what is the maximum magnification of a light microscope

about x1,500

whats the maximum resolution of a light microscope

about 0.2 µm

what is differential staining

using stains that bind differently to cellular components allowing different cell types to be distinguished

why are stains used in light microscopy

to increase contrast and make cellular structures easier to see and distinguish

which stain is used for observing plant cell walls

iodine in potassium iodide which stains starch blue black

which stain should be used to see animal cell components

methylene blue

which chemical stain makes chromosomes appear red

acetic orcein

which chemical stain makes cytoplasm appear pink

eosin

what are artefacts

objects or structures seen through a microscope that have been created during the preparation of the specimen

how do you prepare a wet mount sample in 4 steps

use a pipette and add a small drop of water to the centre of a clean glass slide, use a pair of forceps to place a thin section of specimen onto the drop of water, add a few drops of stain to the specimen, slowly lower cover slip at a 45 degree angle to the specimen

why do you lower the cover slip at an angle

to minimise air bubbles

how do electron microscopes form images

using a beam of electrons

why do electron microscopes have a higher resolution than light microscopes

a beam of electrons has a much shorter wavelength than a beam of visible light

what is the resolution of transmission electron microscopes

about 0.5 nm

what is the magnification of transmission electron microscopes

about x1,500,000

how do TEM work

electromagnets transmit a beam of electrons through a very thin specimen to produce an image of its internal ultrastructure

why do some parts of the image appear darker using TEM

denser regions absorb more electrons so fewer electrons reach the detector

what type of image does a TEM produce

2D black and white image

what are disadvantages of electron microscopes

expensive, images are monochrome, complex specimen preparation and specimens must be dead

how do SEM work

a beam of electrons scans the surface of a specimen and reflected electrons are used to form an image

what type of image does an SEM produce

3D image

what type of cells can be viewed with a SEM and a TEM

non-living cells

why can’t electron microscopes observe living cells

they require a vacuum and complex specimen preparation so the specimen can’t stay alive

what type of cells can be viewed with a light microscope

living and non-living cells

why is a vacuum necessary for SEM and TEM

so electrons don’t collide with air molecules and ensure the electron beam travels in a straight line

what is the magnification for a scanning electron microscope

about x1,500,000

what type of image does a SEM produce

3D monochrome image showing the surface of the specimen

what is the resolution for a scanning electron microscope

about 5 nm

describe the structure of a cell-surface membrane

a phospholipid bilayer containg proteins and cholesterol

what are the functions of the cell-surface membrane (2)

to control movement of substances into and out of cell and contains receptor proteins involved in cell signalling

what is the function of the nucleus

contains the cell’s genetic material and controls activities of the cell through gene expression

what is a chromatin

DNA associated with proteins forming the material from which chromosomes are made

what is the function of the nucleolus

site of rRNA synthesis and ribosome assembly

what is the nuclear envelope

double membrane that surrounds the nucleus separating the nuclear contents from the cytoplasm

what are nuclear pores

openings in the nuclear envelope which allow substances like mRNA to move between nucleus and cytoplasm

what is the rough endoplasmic recticulum’s structure

a network of membrane bound cisternae covered in ribosomes continuous with the nuclear envelope

what are cisternae

flattened membrane bound fluid filled sacs

what is the function of the rough endoplasmic recticulum

provides a surface for ribosomes to synthesise proteins and transports proteins within its cisternae

what is function of ribosomes

site of translation and protein synthesis

what are ribosomes made of

proteins and rRNA

what are 80S ribosomes

larger ribosomes found in the cytoplasm of eukaryotic cells

where can ribosomes be found

attatched to the rough endoplasmic recticulum or free in the cytoplasm

describe the structure of the smooth endoplasmic recticulum

a cisternae network with no ribosomes attached to its surface

what is the function of the smooth endoplasmic recticulum

lipid synthesis and processing of certain substances

describe the structure of the golgi apparatus

stacks of flattened cisternae surrounded by many small golgi vesicles

what is the function of the golgi apparatus

to modify, sort and package proteins into vesicles for transport

what else can the golgi apparatus produce

lysosomes

what are lysosomes

membrane bound vesicles that contain hydrolytic enzymes

why is the membrane in lysosomes important

it prevents the hydrolytic enzymes inside from spilling out and digesting the cells own contents

whats the function of lysosomes

to hydrolyse unwanted materials, worn-out organelles and engulfed pathogens

what is the name for one mitochondria

a mitochondrion

what is the structure of a mitochondrion

a double membrane, inner membrane folded into cristae, intermembrane space and a matrix

whats the function of mitochondria

to produce ATP for cellular processes and the site of aerobic respiration

what is the outer mitochondrial membrane

separates the mitochondrial contents from the cytoplasm

what is the inner mitochondrial membrane

folded into cristae to increase surface area for proteins involved in aerobic respiration and ATP production

what is the matrix

fluid filled interior containing enzymes, mitochondrial DNA and 70S ribosomes

what is the cytoskeleton

network of protein fibres that are present throughout the cytoplasm and provide structure and support to the cell

what are the 3 main components of the cytoskeleton

microfilaments,microtubules and intermediate filaments

what are microfilaments

solid strands made of actin involved in cell movement

what are microtubules

hollow strands made of tubulin which form a scaffold like structure throughout the cell

what are the 2 main functions of microtubules

form a key part of the mitotic spindle in cell division and help transport vesicles and organelles within cells

what do intermediate filaments do

maintain the position of organelles within cell and provide mechanical strength to certain tissues like skin and hair

what are the main functions of the cytoskeleton?

providing mechanical strength,maintain cell shape,transport organelles and enable cell movement

describe the structure of a plant cell wall

made up of cellulose fibres and contains channels called plasmodesmata which connect adjacent plant cells

what are the functions of the cell wall (3)

provides mechanical support for the cell, maintains the cell shape and prevents the cell from bursting due to high osmotic pressure

describe the structure of the vacuole

contains cell sap and is surrounded by the selectively permeable membrane tonoplast

whats the function of the vacuole

maintains turgor pressure within the cell and keeps the cell rigid and stops the plant wilting

what is the function of chloroplasts

site of photosynthesis

what is the structure of a chloroplast

double membrane enclosing grana,thylakoids,stroma,DNA and ribosomes

what are grana

stacks of thylakoids containing chlorophyll and photosynthetic electron carriers

what is the stroma

fluid filled region containing enzymes for light-independent reactions

how is a chloroplast adapted for photosynthesis

thylakoid membranes provide surface area,chlorophyll absorbs light and stroma contains photosynthetic enzmes

what are centrioles

cylindrical structures made of microtubules found in the centrosome

what is the function of centrioles

to organise microtubules and the formation of spindle fibres during cell division

what are cilia

short numerous hair like projections containing microtubules that extend from the cell surface

what is the structure of a eukaryotic cillium

membrane bound projection containing a 9+2 arrangement of microtubules

what’s the function of cilia

beat rhythmically to move substances across the cell surface

give an example of where cilia are found

ciliated epithelial cells lining the trachea and bronchi

how do cilia help protect the respiratory system

they move mucus containing trapped particles towards the throat

what is a eukaryotic flagellum

long membrane bound projection with 9+2 arrangement of microtubules

whats the function of eukaryotic flagellum

to produce movement of the cell by beating

give an example of a cell with a flagellum

sperm cell

how do cilia and eukaryotic flagella differ

cilia are short and numerous whereas flagella are longer and fewer

what is a prokaryotic cell

a cell without a nucleus or membrane bound organelles like bacteria

what is the bacterial chromosome

a single circular DNA molecule located in the nucleoid region of the cytoplasm

what are the features of prokaryotic flagellum

made of protein, not 9+2 and rotates to propel the bacterium