A2.2 Cell Structure

What does Cell Theory state

• all organisms are composed of one or more cells

• cells are the smallest unit of life

• all cells come from pre-existing cells

Define Magnification

The increase in an object’s image size compared to its actual size

Define resolution

The minimal distance between two points at which they can still be distinguished as two

Convert 12m into millimetres

12 000mm

convert 350mm into μm

350 000μm

Convert 5.2μm into nm

5 200nm

Explain how a light microscope works

They use light, passing though living or dead specimens, to form an image (might include the use of stains/dyes)

Explain how an electron microscope works

They provide the greatest magnification and resolution. These use electrons passing through a specimen to form an image.

Sate the advantages of a light microscope

• Inexpensive to purchase and operate

• Simple and easy

• Specimens may be living or dead

State the disadvantages of the light microscope

• only magnifies up to 2000

• Has a low resolution

State the advantages of an electron microscope

• Magnifies over 500 000x

• High resolution

State the disadvantages of an electron microscope

• Expensive to purchase and operate

• complex specimen preparation

• specimens must be dead

What are the two types of micrometer

Stage and ocular

How is the ocular micrometre used in relation to the stage micrometre

The stage micrometre needs to be calibrated to the ocular one

Why can you not simply use the ocular micrometre to determine cell size?

Because the units are arbitrary.

What is often used with a micrograph to determine cell size?

A scale bar

What is the magnification equation

Magnification = Image size / Actual size

What are the 2 general types of electron microscopes

Scanning electron microscopes (SEM) and transmission electron microscopes

How do SEMs work?

Use a beam of electrons to scan the surface of the specimen

How do TEMs work?

Use a beam of electrons through a thin section of the specimen in order to view it’s inner structure

What are the two preparation techniques used for EMs?

Freeze fractioning and cryogenic electron microscopy

Define the process of freeze fracturing

Rapid freeze a dead specimen and physically breaking down the specimen (fracturing)

Define the process of cryogenic electron microscopy

Allow the image to be formed using computer enhancement that show 3D fragments of cells

What microscope can you look at live specimens

Light microscope

What are the two stains that are used in light microscopes

Fluorescent stains/dyes and/or immunofluorescence

How do fluorescent dyes work

They combine with a particular cellular component. When eradicated with UV or violet-blue light, the components fluoresce

How does immunofluorescence work

Some antibodies are already combined with dyes, specific molecules combine with target cells, when irradiating in a specific light, we can detect the target cells

What are 3 things all cells have

• Cytoplasm

• DNA

• Plasma Membrane

Why is DNA important in cells?

Allows cells to create new cells due to DNA replication

Where is cytoplasm found?

In the boundary of the cell

What is cytoplasm composed of?

Cytosol, a fluid mainly composed of water with dissolved substances such as ions

Where do most of the cells important reactions occur?

In the cytoplasm

Where is the cell membrane found?

The cell membrane is found surrounding the cell and enclosing it’s content

What number of layers is present in the membrane?

2

What is the role of the plasma membrane?

To control the cells interactions with the exterior, to ensure the uptake of required materials into the cell and the removal of waste from the cell

What type of molecule is found throughout the cell membrane?

Proteins

What are the three roles of proteins in the cell membrane?

• Cell communication

• Cell recogniton

• The transport of materials in and out of cells

What features are always present in a prokaryote cell?

• A cell wall

• Cell surface membrane

• Circular loop of naked DNA

• 70s Ribosomes

• Cytoplasm

What are features of a prokaryotic cell which aren’t always present?

• A capsule

• A plasmid

• Infoldings of the cell membrane

• pili

• flagellum

Draw a prokaryotic cell

What are the two types of organism

archaea and bacteria

How big are prokaryotic cells?

Less than 1 micrometer

Is a prokaryote or a eukaryote cell bigger?

Eukaryote

Define the role of ribosomes

they bind and read mRNA during translation to produce proteins

Define the role of naked circular DNA

They contain genetic material

Define the role of plasmids

Loops of dna seperatefrom circular DNA but also carry genes

Define the role of the cytoplam

The site of cellular reactions, main component is cytosol

Define the role of the cell membrane

controls what enters and exits the cell

Define the role of the cell wall

Made up of peptoglycan, and maintains the shape and supports the cell

Define the role of capsule

prevents bacteria from drying out and protects the cell during attacks from other cells

Define the role of the flagellum

Long tail like structure that allow bacteria to move

Define the role of pili

Shorter and thinner than flagella, allows adherence between cells

What are the 16 features of an animal eukaryotic cells

1. Plasma membrane

2. 80s ribosomes

3. Golgi Apparatus

4. vesicles

5. nucleus

6. nucleolus

7. nuclear pore

8. rough endoplasmic reticulum

9. cytoskeleton

10. vacuoles

11. lysosomes

12. smooth endoplasmic reticulum

13. centrioles

14. nuclear membrane

15. mitochondria

16. cytoplasm

Draw an animal eukaryotic cell

Define the role of the golgi apparatus

stores, packages, and modifies proteins

Define the role of the nuclear pore

allows communication between the nucleus and the rest of te cell

Define the role and structure of the nucleolus

A dense, solude structure involved in ribosome synthesis

Define the role of rough endoplasmic reticulum

site of proteins synthesis

What is the difference between sER and rER?

sER = rER - ribosomes

Define the role and structure of lysosomes

sacs bounded by a single membrane and contains transport enzymes

Define the role and structure of centrioles

composed of microtubules and associated with nuclear division

What is the name of the area where centrioles are found?

A centrosome

What type of free ribosome do you find in eukaryotes?

80s

What type of ribosome do you find in mitochondria?

70s

What type of free ribosome do you find in prokaryotic cells?

70s

Draw a eukaryotic plant cell

Define the function of a central vacuole

It has storage and hydrolytic functions

Define the function of chloroplasts

Contain chlorophyll and is the site of photosynthesis

Define the cell wall

a semi-rigid structure mainly composed of cellulose

define the endoplasmic reticulum

a network of tubes and flattened sacs which connects with the plasma membrane

Define metabolism

The sum of all the chemical reactions that occur within an organism

Define homeostasis

maitaining a constant internal environment

Define the exterior of the cell in a plant, animal, and fungal cell

Plant: a cell wall with cellulose + plasma membrane

Animal: Plasma membrane

Fungal: a cell wall with chitin + plasma membrane

Define vacuoles in the cell in a plant, animal, and fungal cell

Plant: large vacuoles for the production of carbohydrates

Animal: when present, vacuoles are small and numerous

Fungal: when present, vacuoles are small and numerous

How do plant cells store carbs?

as starch

How do animal and fungal cells store carbs?

as glycogen

Give an example of an atypical structure in a specialised cell

the number of nuclei

What are the two stypes of hyphae?

Septate hyphae and aseptate hyphae

Which type of hyphae contains more than one nuclei?

Aseptate

Name the cell which has no nucleus in the body

A red blood cell

How are muscle cells adapted?

there isn’t that much cell membrane so the cells are tubular and merge together therefore having multiple nuclei

What is the mneumonic to remember the evidence for endosymbiosis in mitochondria and chloroplasts?

Mad Dr.

Membranes

Antibiotics

Division

DNA

Ribosomes

Using the mneumonic mad dr. what is the evidence of endosymbiosis in mitochondria and chloroplasts?

Membranes: they have a double membrane

Antibiotic: they are both susceptable to antibiotics like bacteria

Division: divide by binary fission like bacteria

DNA: has its own DNA which is naked and circular

Ribosomes: have their own ribosomes which are 70s

Explain the theory of how complex eukoryatic cells were create through endosymbiosis

2 billion years ago a larger cell that had a nucleus and was capable of sexual reproduction, engulfed a smaller prokaryotic cell that could produce energy, they developed a mutually beneficial relationship called endosymbiosis

What process allows specialisation within the cell?

Compartmentalisation