2.1 Cell structure

what is magnification?

the number of times larger an image appears, compared with the size of the object

what is resolution?

the clarity of an image, the higher the resolution the clear the image

what is a light/optical microscope?

it uses visible light and lenses

what wavelength of visible light do optimum microscopes use?

400-700 nm

what happens to structures closer than 200nm (0.2um) when using an optical microscope?

they appear as one object because the wavelength of visible light ranges from 400-700 nm

why are optical microscopes used a lot in schools and hospitals?

they are:

relatively cheap

easy to use

portable

can study living specimens

what magnification do optimum microscopes allow?

x 1500

why can’t optimum microscopes magnify any further?

because their resolution is limited, they cannot magnify any higher while still giving a clear image

what is the calculation for magnification?

total magnification= magnifying power of the objective lens x magnifying power of the eyepiece lens

what is a photomicrograph?

a photograph of the image seen using an optical microscope

how do laser scanning/confocal microscopes work?

they use laser light to scan an object point by point and assemble it into one image

what is the quality of laser scanning microscopes?

the images are high resolution and show high contrast

how do electron microscopes work?

the electrons are fired from a cathode and focused, by magnets rather than glass lenses, onto a screen or photographic plate

what wavelength do the electrons in electron microscopes use?

0.004 nm

what is the quality of electron microscopes?

they have much greater resolution than optical microscopes and can give clear and highly magnified images

how much smaller of a wavelength do the fast travelling electrons have compared to the central part of the visible light spectrum?

125 000

how do transmission electron microscopes (TEM) work?

the specimen has to be chemically fixed by being dehydrated and stained

the beam of electrons passes through the specimen and focus on the screen

what image do transmission electron microscopes produce?

a black and white 2D image

what is the photograph from a transmission electron microscope called?

electron micrograph

what magnification do transmission electron microscopes have?

up to 2 million times, and new ones can magnify up to 50 million times

how do scanning electron microscopes work?

electrons don’t pass through the specimen, which is whole, but cause secondary electrons to bounce off the specimens surface and are focused on a screen

what image do scanning electron microscopes produce?

black and white 3D image, but colour can be added using computer programmes

what magnification do transmission scanning microscopes have?

15 000-200 000

what has to be done to the specimen for a scanning electron microscope?

the specimen has to b placed in a vacuum and is often coated with a fine film of metal

which microscopes require dead specimens in a vacuum?

electron microscopes

why are electron microscopes less practical?

are large and very expensive

need a lot of skill and training to use

what is the nucleus surrounded by?

a double membrane called the nuclear envelope, which has pores

what does the nucleolus contain and make?

it contains RNA and doesn’t have a membrane around it

it is where ribosomes are made

what is chromatin?

the genetic material, consisting of DNA wound around histone proteins

what do pores allow?

for enable larger substances, such as messenger RNA (mRNA) to leave the nuclear

what do chromosomes contain?

the organism’s genes

what is the nucleus?

the control centre of the cell

stores the organism’s genome

transmits genetic information

provides the instructions for protein synthesis

what is the endoplasmic reticulum?

a system of membranes, containing fluid-filled cavities (cisternae) that are continuous with the nuclear membrane

what is the rough endoplasmic reticulum (RER)?

it is coated with ribosomes

what are cisternae?

fluid filled cavities that are part of the rough endoplasmic reticulum

how is RER the intracellular transport system?

the cisternae form channels for transporting substances from one area of a cell to another

what is the smooth endoplasmic reticulum (SER)?

there are no ribosomes on its surface

what does the SER contain?

enzymes that catalyse reactions involved with lipid metabolism

what is SER involved in?

with absorption, synthesis and transport of lipids (from the gut)

what is the golgi apparatus?

a stack of membrane-bound flattened sacs

what is the function of the golgi apparatus?

to modify proteins and package them into the vesicles

what is the size and shape of mitochondria?

can be spherical, rod-shaped or branched, and are 2-5 um long

what is the structure of the mitochondria?

they are surrounded by two membranes with a fluid fill space between them

the inner membrane is highly folded into cristae

the inner part of the mitochondrion is a fluid-filled matrix

what are the mitochondria?

the site of ATP production during aerobic respiration

what do the mitochondria do if the cell needs more energy?

self-replicate, so more can be made if the cell’s energy need to increase

what is the size of chloroplasts?

they are large organelles, 4-10 um long

where are chloroplasts found?

they are only found in plant cells and some protoctists

what are chloroplasts surrounded by?

a double membrane or envelope

what is the inner membranes structure?

the inner membrane is continuous with stacks of flattened membrane sacs called thylakoids which contain chlorophyll

what are thylakoids?

stacks of flattened membrane sacs

what are each stack or pole of thylakoids called?

a granum (plural is grana)

what is the stroma?

the fluid-filled matrix

what do chloroplasts contain?

loops of DNA and starch grains

what is the function of chloroplasts?

the site of photosynthesis

flagellum

flagella on eukaryotic cells are like cilia but longer. they stick out from the cell surface and are surrounded by the plasma membrane

inside they have two microtubules in the centre and nine pairs around the edge

→the microtubules contract to make the flagellum move. this movement propels cells forwards

chloroplasts

a small, flattened structure found in plant cells. it is surrounded by a double membrane, and also has membranes inside called thylakoid membrane

these membranes are stacked up in some parts of the chloroplast to form grana. grana are linked together by lamella- thin, flat pieces of thylakoid membrane

→the site of photosynthesis. some parts happen in the grana and others in the stroma (a thick fluid)

centriole

small, hollow cylinders, made of microtubules. found in animal cells, but only some plant cells

→involved in the separation of chromosomes during cell division

golgi appartus

a group of fluid-filled, membrane-bound, flattened sacs. vesicles are often seen at the edge

→it processes and packages new lipids and proteins and makes lysosomes

ribosome

a very small organelle that either floats free in the cytoplasm or is attached to RER. it is made up of proteins and RNA. it is not surrounded by a membrane

→the site where proteins are made

plasma membrane

the membrane found on the surface of animal cells and just inside the cell wall of plant cells. it is made mainly of lipids and proteins

→regulates the movement of substances into and out of the cell. it also has receptor molecules on it, which allows it to respond

cell wall

rigid structure that surrounds plant cells. it is made mainly of the carbohydrate cellulose

→supports plant cells

mitochondrion

it’s usually oval-shaped. it has a double membrane- the inner one is folded to form structures called cristae

inside is the matrix, which contains enzymes involved in respiration

→the site of aerobic respiration, where ATP is produced. mitochondria are found in large number in cells that are very active

cilia

hair-like structures found on the surface membrane of some animal cells. in cross-section, they have an outer membrane and a ring of nine pairs of protein microtubules inside, with a single pair of microtubules in the middle

→the microtubules allow the cilia to move. this movement is used by the cell to move substances along the cell surface

nucleus

a large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. the nucleus contains chromatin- DNA and proteins. it also contains the structure called the nucleolus

→the nucleus controls the cell’s activities. the DNA contains instructions to make proteins. the pores allow substances to move between the nucleus and the cytoplasm. the nucleolus makes ribosomes

rough endoplasmic reticulum

a system of membranes enclosing a fluid-filled space. the surface is covered with ribosomes

→folds and processes proteins that has been made at the ribosomes

smooth endoplasmic reticulum

a system of membranes enclosing a fluid-filled space with no ribosomes

→synthesises and processes lipids

lysosomes

a round organelle surround by a membrane, with no clear internal structure

→contains digestive enzymes. these are kept separated from the cytoplasm and are used to digest invading cells or break down worn out components of the cell