AQA A Level Biology - Cell Structure

List all the organelles found in all eukaryotic cells.

• centrioles

• rough endoplasmic reticulum

• smooth endoplasmic reticulum

• nucleus

• ribosomes

• cell-surface membrane

• lysosome

• golgi apparatus + vesicules

• mitochondria

which organelles do only plant cells contain?

• chloroplasts

• cell wall

• permanent vacuole 

what is organelle 1?

chloroplast

what is organelle 2?

cell wall

what is organelle 3?

cell membrane

what is organelle 4?

cytoplasm

what is organelle 5?

permanent vacuole

what is organelle 6?

nucleolus

what is organelle 7?

nuclear envelope

what is organelle 8?

nucleoplasm

what is organelle 9?

rough endoplasmic reticulum

what is organelle 10?

ribosome

what is organelle 11?

mitochondrion

what is organelle 12?

golgi body 

what is organelle 13?

lysosome

what is organelle 14?

smooth endoplasmic reticulum 

describe the structure of the Nucleus

• it is a membrane bound organelle, containing a nucleolus and chromatin (DNA stored in the nucleus in an uncoiled form), which are contained in the nucleoplasm

• it has a double membrane called the nuclear envelope which has small holes in called the nuclear pores

• the outer nuclear membrane is continuous with RER membranes 

• largest organelle 

describe the function of the nucleus

• envelope encloses and protects DNA

• nuclear pores allow entry and exit of substances such as nucleotides and mRNA

• chromatin condenses to form chromosomes for cell division, produces semi-complete ribosomes, coenzymes, nucleotides, proteins

describe the structure of the mitochondria

• double membrane 

• inner membrane folded to form cristae

• the space in between the cristae is called the matrix and is filled with fluid 

• the mitochondrion contains ribosomes (70S, smaller) , DNA and enzymes

describe the function of the mitochondria

• site of aerobic respiration, release energy and synthesise ATP

• enzymes in matrix catalyse reactions

• cristae hold these enzymes in place

• produce some of the proteins they require (ribosomes)

• cristae also increase surface area for aerobic respiration + metabolic reactions

describe the structure of the rough endoplasmic reticulum

• system of hollow tubes and sacs, that are interconnected and flattened

• covered with ribosomes

• channels are called cisternae

describe the function of the rough endoplasmic reticulum

• folds and processes proteins that have been made at the ribosomes

• cavities of RER allow for transport of proteins 

describe the structure of the smooth endoplasmic reticulum

system of hollow tubes and sacs, that are interconnected and flattened

describe the function of the smooth endoplasmic reticulum

• synthesises and processes lipids

• modifies substances such as steroid hormones

describe the structure of the golgi body

• flattened cisternae - fluid filled membrane bound cavities/sacs - which are stacked on top of each other

• connected to RER

• has vesicles at edge

describe the function of the golgi body

• processes and packages new lipids and proteins - modifies them before secretion (proteins)

• makes lysosomes

• cells that secrete a lot of enzymes contain a lot of RER and golgi apparatus

describe the structure of the golgi vesicles

• small fluid filled sacs in the cytoplasm surrounded by a membrane

• stores lipids and proteins made by the golgi apparatus and transports them out of the cell

describe the structure of the ribosomes

• made up of a small subunit and a large subunit 

• made of rRNA and protein 

• float free in the cytoplasm or are attached to the RER 

describe the function of ribosomes

• site of protein synthesis and thus function relates to the steps of this

describe the structure of the lysosomes

• vesicles that contain hydrolytic enzymes/digestive enzymes

• type of golgi vesicle

• membrane-bound

describe the function of the lysosomes

• contains digestive enzymes called lysozymes - kept separate from cytoplasm by the membrane 

• can be used to digest cellular waste or invading cells

describe the structure of the chloroplasts

• bound by a double membrane 

• contains membranes called thylakoid membranes

• membranes are stacked up in some parts of the chloroplast to form grana 

• grana are linked by lamellae - thin, flat pieces of thylakoid membrane 

• contains thick fluid called stroma 

• contain some DNA

describe the function of the chloroplast                   

• site of photosynthesis - some parts take place in grana, others in stroma

• grana allow a large surface area for the assembly of chlorophyll and so photosynthesis

describe the structure of the cell membrane

• found either on the surface of the cell or just inside the cell wall

• made of a phospholipid bilayer and protein

describe the function of the cell membrane

• regulates movement of substances into and out of the cell

• has receptor molecules on out allowing it to respond to hormones 

describe the structure of the cell wall

• plants and algae - made of cellulose

• microfibrils are embedded in a background material of pectin

describe the function of the cell wall

• maintains the shape of the cell and allows it to remain turgid when water moves into it by osmosis, preventing it from bursting

describe the structure of the cell vacuole

• membrane bound organelle

• contains cell sap

• membrane is called tonoplast

describe the function of the cell vacuole

• maintains pressure inside the cell and keeps it rigid

what is the formula for magnification?

magnification = size of image/size of real object

define the term magnification

the number of times larger an image is compared with the real size of an object

define the term resolution

the ability to distinguish between two separate points

what is the limit of resolution of a light microscope?

• ½ the wavelength of the radiation used to view the specimen

• the shortest wavelength of light is 400nm so the max resolution is 200nmwha

what does a light microscope look like?

what is the maximum useful magnification of an optical microscope?

x1500

which organelles can you not see using a light microscope?

• ribosomes

• lysosomes

• mitochondria 

• endoplasmic reticulum

what is the other kind of microscope?

electron microscopes

what are the two types of electron microscope?

• transmission electron microscope

• scanning electron microscope

what is the maximum resolution of a transmission electron microscope?

0.1nm

what is the maximum resolution of a scanning electron microscope?

20nm

describe how a TEM works

• use electromagnets to focus a beam of electrons, which are transmitted through the specimen

• denser parts of the specimen absorb more electrons, making them look darker on the resulting image

describe how an SEM works

• scan a beam of electrons across a specimen

• this knocks off electrons from the specimen

• these are gathered in a cathode ray tube to form an image 

• the resultant images show the surface of the specimen and the 3-D

what are the advantages of TEMs?

gives the highest resolution images so shows small objects

what are the advantages of SEMs?

• can be used on thick specimens

• produce 3D images

• have a relatively high resolution

what are the disadvantages of TEMs?

• can only be used on very thin specimens

• can only be used on non-living specimens

• the specimen must be viewed in a vacuum

• images may contain artefacts which can make it difficult to identify organelles

what are the disadvantages of SEMS?

• give lower resolution images than TEMs

• can only be used on non-living specimens

• need to be used in a vacuum

• images may contain organelles

describe how to prepare a temporary microscope slide

• place a small drop of water on the centre of the slide

• use tweezers to place a thin section of your specimen on top of the water drop

• add a drop of iodine on top

• place a coverslip on top

• blot off any excess iodine using filter paper 

which organelles do prokaryotic cells (mainly bacteria) contain?

• cell wall

• slime capsule

• plasmid

• circular DNA

• flagellum

• cytoplasm

• cell membrane

• small ribosomes (70S vs 80S)

which organelles do prokaryotic cells not contain?

• any membrane-bound organelles

• mitochondria

• nucleus

• ERs

• golgi apparatus

• lysosomes

describe the structure of a prokaryotic cell wall

• made of murein, which is a glycoprotein (protein with carbohydrate attached) - peptidoglycan

describe the function of the cell wall

• physical barrier that protects against mechanical damage

• excludes certain substances from the cell

describe the structure and function of the slime capsule

• coats the cell wall, made up of secreted slime

• protects the bacteria from attack by cells of the immune system

• helps bacteria stick together

describe the structure and function of the flagellum

• has a rigid, corkscrew shape and a rotating base

• this helps the cell spin through fluids

describe the structure and function of prokaryotic enzymes

• smaller than eukaryotic - 70S type

• site of protein synthesis - can be inhibited by certain antibiotics

• the difference between prokaryotic and eukaryotic ribosomes allows antibiotics to selectively target prokaryotes 

describe the function of the circular DNA

possesses the genetic information for the replication of bacterial cells

describe the function of the plasmids

• can reproduce independently, so are used as vectors in genetic engineering

• possess genes that aid the survival of bacteria by producing enzymes that can break down antibodies

describe the structure of viruses

• they have a core of genetic material (DNA or RNA)

• this is covered by a protein coat called a capsid

• attachment proteins stick out from the capsid 

describe how viruses reproduce

• virus attaches to the host cell receptor proteins

• virus injects genetic material into the host cell

• genetic material and proteins are replicated by the host cell machinery - ribosomes, RER

• the viral components assemble 

• the replicated viruses are released from the host cell

• the attachment proteins on the virus require different receptor proteins, affecting which types of host cell viruses can infect