biology

what are the 3 cell theory

1. all living organisms are composed of one or more cells

2. cells are the basic unit of life

3. all cells come from preexisting cells. These principles form the foundation of cell theory, illustrating the fundamental biological role of cells.

unicellular organisms

single cells that performs all life functions (characteristic of life) - can be prokaryotic and eukaryotic

multicellular organisms

two or more cells. ALWAYS eukaryotic (contain nucleus and membrane-bound organelles)

division of labor order

1. cells group together to form tissues

2. group of tissues form organs

3. group of organs form organ systems

• allows organism to grow larger and live longer

processes of life in unicellular organisms

MRS GREN

M

R

S

G

R

E

N

M - movement

R - respiration

S - sensitivity

G - growth

R - reproduction

E - excretion

N - nutrition

movement

ability to change position or move parts of the organisms

respiration

chemical reactions that release usable energy from nutrients

sensitivity

ability to detect and respond to changes in environment

growth

permanent increase in size or cell mass

reproduction

production of new organisms

excretion

removal of metabolic waste products

nutrition

obtaining or producing substances needed for energy, growth, and survival

unicellular organisms

concist of only one cell, but that single cell carries out all function needed for life. it does not need organs or organ systems because the cell itself acts as the entire organism.

where does respiration take place in prokaryotic cells

respiration takes place in the cytoplasm of prokaryotes cell because they do not have mitochondria

access to genetic material in prokaryotic unicellular cell

genetic material is not enclosed in nucleus. it is located in the nucleoid region of the cytoplasm = so ribosome have relatively direct access to the genetic material needed to make protein.

magnification

how much larger an object appears compared with its actual size

resolution

ability to distinguish between two objects that are very close together as seperate objects

smaller resolving power =

= better resolution

coarse adjustment khob

rough focus

moves the objective lens/stage a larger distance to acheive rough focus. used mainly at low magnification

fine adjustment knob

makes very small movements to obtain sharp, precise focus, especially at high magnification

how do you develop a temporary mound of cells or tissues.

Basic procedure

1. Obtain a thin sample of cells/tissues.

2. Place the sample in the center of a clean microscope slide.

3. Add a drop of water or appropriate liquid.

4. If necessary, add a stain to increase contrast.

5. Carefully lower a coverslip at an angle using a mounted needle/probe. 

6. Lower it slowly to reduce the formation of air bubbles. 

7. Remove excess liquid with filter paper if necessary.

8. Place the slide on the microscope stage. 

why use stain?

most cells are relatively transparent = little contrast between structures

stain:

• increases contrast

• makes structures easier to distinguish

• can allow particular structures to become visible

why must sample be thin?

easier for light to pass through specimen = easier to see/clearer image

light microscope advantage + disadvantage

living cells + color, but lower resolution

disadvantage: cannot reveal small structures such as

• ribosomes

• viruses

• detailed membrane structures

fluorescent light microscope

highlight particular structures or molecules. a fluorescent stain/label is attached to the target —> meet light —> make the target visible against darker background

advantage:

• specific structure/moleucles can be highlighted

• strong contrast

• useful for locating specific molecules within cell

disadvantage:

• resolution remains limited (light)

• fluorescent labels can fade over time

• can be expensive

immunofluorescence microscope

antibody + antigen

antibody is designed to bind to a specific antigen, often a particular protein. the antibody is linked to a fluorescent dye or secondary antibody is used.

• to locate specific protein or antigen

advantage:

• highly specific

• can locate particular proteins/molecules

disadvantage

• cells have to be fixed (chemically killed and frozen in place)

• antibody binding may not alwys be perfectly specific

• suitable antibodies can be expensive

differences between fluorescent stains and immunofluorescence

fluorescent stain: labels a structure/molecules so it can be seen

immunofluorescence: uses the specific binding of antigens to locate a particular molecule, usally a protein

electron microscope

• high resolution + magnification

• specimen must be killed and undergo chemical treatment

• cannot observed living organisms

• beam of electrons - with shorter wavelengths than visible light

freeze fracture (electron microscope)

frozen and then physically fractured in the center to look at its internal. the fracture often occurs along the plane of the membrane, allowing scientists to examine the internal organization of membrane.

• preserve structures close to their natural arrangement through rapid freezing.

advantage:

• studying membrane organization

• usefulf or seeing:

  • membrane proteins

  • their distribution

  • the overall structure of large membrane surfaces

disadvantage:

• freezing can damage/distort structures

• living processes cannot be observed

• limited infomation about non-membrane structures.

cryogenic electron microscope (cryo-EM)

more advanced form of electron microscope

Cryogenic Electron Microscopy (Cryo-EM)  A more advanced form of electron microscopy.  -frozen at extremely lower temperatures so that their structure can be studied in a state close to their natural/native arrangement.  advantage: extremely high resolution 3D structural information viruses and protein complexes preserve specimen in relatively near native state disadvantage very expensive specialist preparation sufficiently thin or small electron beams can damages samples

structures common in ALL cells (4)

1. plasma membrane

2. cytoplasm

3. ribosomes

4. genetic material (DNA)

plasma membrane

• phospholipid bilayer

• regulates what enters and leave the cell

• compartmentalization = separates the inside of the cell from its external environment

cytoplasm

holds cell parts, site for metabolic reactions (ex. glycolysis), transport

ribosomes

site of protein synthesis

mRNA —> protein

(read insturctions on mRNA and use them to build proteins)

location:

1. cytoplasm

2. rough endoplasmic reticulum

structure:

half ribosomal RNA (rRNA) and half protein.

size of ribosome in prokaryotic cell

70S

size of ribosome in eukaryotic cell

80S

location of genetic material

1. prokaryotic

2. eukaryotic

Prokaryote:

DNA → usually one circular chromosome + possibly small plasmids → no nucleus (nucleoid region)

Eukaryote:

DNA → multiple linear chromosomes → inside a nucleus

prokaryote

• no nucleus

• no membrane-bound organelles

two major group of prokaryotes

1. bacteria

2. archaea

What are cell structures of a typical prokaryote?

1. capsule

2. cell wall

3. plasma membrane

4. cytoplasm

5. nucleoid

6. plasmids

7. ribosomes

8. phili

9. flagellum

capsule (pro)

protection against environment conditions and attachment to surfaces

• not every prokaryote has capsule

cell wall (pro)

maintain shape and protect the cell

• shape

• structural support

• prevents the cell from bursting due to water entering by osmosis.

most bacteria:

• peptidoglycan

cell wall for bacteria

peptidoglycan

cell wall for plants

cellulose

cell wall for fungi

chitin

plasma membrane (pro)

because no mitochondria, plasma membrane is involved in aerobic respiration.

Plasma membrane → controls transport and provides a surface for processes such as respiration.

nucleoid (pro)

region containing the main DNA molecule fo prokaryote

NOT nucleus

main pro chromosomes is usually:

• circular

• double-stranded DNA

• one main chromosome

plasmids (pro)

small circular DNA molecules carrying additional genes

ex. may carry a gene for antibiotic resistance

importance of plasmids

If bacteria acquire an antibiotic-resistance gene:

Plasmid → antibiotic resistance → greater survival → resistance gene can spread 

(horizontal gene transfer)

pili (pro)

attachment - some transfer DNA

• attachment to surfaces

• attachment to other cells

sex pilus

some bacteria have specialized pili involved in conjugation (transferring DNA between bacteria)

This allows DNA, often plasmid DNA, to be transferred between bacteria. 

increases genetic variation (horizontal gene transfer)

flagellum (in both eu and pro)

movement

• rotates, allowing the entire cell (bacteria) to move through liquid

eukaryotic cells

has a nucleus surrounded by nuclear envelope and membrane-bound organelles

ex.

• animals

• plants

• fungi

• protists

What are cell structures of a typical eukaryote? 

1. plasma membrane

2. cytoplasm

3. nucleus

4. ribosomes

5. mitochondria

6. rough endoplasmic reticulum

7. smooth ER

8. golgi apparatus

9. vesicles

nucleus

controls cell activities by containing the cell’s genetic information

nuclear envelope

double membrane surrounding the nucleus

nuclear pores + nucleolus + chromatin

Nuclear pores 

Opening that controls movement of substances between the nucleus and cytoplasm. 

• mRNA

• Proteins

• Other molecules

Nucleolus

Site where ribosome components are produced/assembled. 

Chromatin 

DNA associated with proteins

Before cell divisions:

Chromatin condenses → chromosomes 

mitochondria

site of aerobic respiration —> ATP production

cristae - folds of inner membrane

= increases the surface area available for reactions involved in aerobic respiration

rough ER

synthesis/processes proteins

smooth ER

• involved in lipid production/synthesis

• forms transport vesicles

golgi apparatus

modifies, sorts, and packages proteins into vesicles

vesicles

transport substance

lysosomes (ani)

contains digestive enzymes that digest worn out cell components and foreign particles

cilia (eu)

move substance across cell surface

vacuoles (ani and plant)

plant: stores ater, maintain turgor pressure

animal: small sacs, store water, nutrients, and waste

fungi: stores substancs, help with degradation and maintain cell conditions

whya re fungi not plants?

• have cell wall made of chitin, not cellulose

• do not have chloroplast

• do not photosyntehsis

• obtain nutrietns by secreting enzymes and absorbing the digested products

atypical cell

1. skeleton muscle cell

2. red blood cells

3. phloem sieve tube element

skeletal muscle clel

contraction

• extremely long, contain many nuclei, and have many mitochondria.

• long shape allows them to form long muscle fibres that contract along their length.

• many mitochondria provide ATP for repeated muscle contraction.

red blood cells

transport oxygen

• no nucleus (to make room for oxygen), lack most organelles, have a biconcave shape

high SA:V ratio + short diffusion distance —> efficient oxygen diffusion

flexible shape —> allows them to pass through narrow capillaries

phloem sieve tube elements

transport dissolved organic nutrients, particularly sucrose through plants

• no nucleus, very little cytoplasm, few organelles

• absence of nucleus and less cytoplasm creates a more open pathway, allowing phloem sap to flow efficiently through the sieve tube.

discrete subunit + specific function

A true membrane bound organelle is a discrete subcellular compartment enclosed by at least one lipid bilayer, which helps isolate its internal biochemical environment from the cytoplasm.

compartmentalization

separating different chemical reactions into different areas of the cell

why separate the nucleus from the cytoplasm

the nuclear envelope separates DNA and nuclear processes from the cytoplasm, allowing transcription and RNA processing to occur in a controlled environment before mRNA moves to ribosomes in the cytoplasm for translation.

advantage of compartmentalization

1. protects and isolates DNA

2. separates transcription and translation

3. different chemical environemnt/conditions an be maintained

compartmentalization advantages

enzymes can be concentrated

• more enyzme molecules are availble to interact with substrates at the same time —> reaction can happen faster

isolate harmful reactions

• prevent them from freely interacting ith everyhting inside the cytoplasm

ex. lysosomes

Phagocytic vacuoles

A phagocytic vacuole is a membrane-bound compartment formed when a cell engulfs a particle, such as a bacterium. The bacterium is isolated inside the vacuole, which can then fuse with a lysosome.

This allows the cell to isolate and digest foreign material without exposing the entire cytoplasm to it.

What is a stem cell?

Unspecialized cell that can:

1. Self-renew → produce more stem cells through cell division. 

2. Differentiate → develop into a more specialized cell type. 

What happens after fertilisation?

Sperm + egg → zygote → repeated cell division (morula stage) → blastocyst  → early embryo → differentiation → different specialized cell types.

Gradients of signalling molecules 

Morphogens: In an early embryo, certain cells secrete “form-giving” molecules called ‘morphogen.” As these morphogens (signalling hormones) diffuse outwards from their source, a gradient is established in the local area.

morphogens

Source → high morphogen concentration → → → low morphogen concentration 

• The further a cell is from the source, the lower the concentration of morphogen it receives. 

How does this affect gene expression?

• Different cells experience different concentrations of morphogens. 

• Different concentrations can cause different genes to be expressed. 

Morphogen gradient → different concentrations received → different gene expression → different differentiation → different specialized cells 

What is the impact of gradients on gene expression within an early-stage embryo?

Morphogens diffuse from a source, creating a concentration gradient. Cells at different distances receive different concentrations of morphogens, causing different genes to be expressed. This leads to different cells differentiating into different specialised cell types.

stem cell niches in adults

A specific environment where adult stem cells are located and maintained. 

The surrounding environment provides signals that influence whether stem cells:

• Remain as stem cells

• Divide

• Differentiate into specialized cells 

stem cell niches (bone marrow)

Bone marrow: stem cells in the bone marrow can produce different types of blood cells.

Ex. Hematopoietic stem cell 

• Red blood cells

• White blood cells

• Platelets 

This allows the body to continuously replace blood cells. 

stem cell niche (hair follicles)

Hair follicles: contribute to the production and replacement of cells involved in hair growth and the hair follicle. 

totipotent

Totipotent = “TOTAL”

Can develop into ALL cell types including: 

• All the cells in the body

• Extra-embryonic tissues (supporting tissues), such as the tissues that helps form the placenta. 

pluripotent

Can develop into many different specialized body cell types, but cannot normally form all the extra-embryonic tissues needed to produce an entire organism.

Multipotent

Can develop into a more limited range of related specialized cells. 

• Adult multipotent stem cells = specialized cells found in their surrounding area. 

unipotent cells

can only produce one specialized cell type (ex. liver cells)

nullipotent

cannot differentiate further

Potency hierarchy

Totipotent = Total

Pluripotent = Plenty

Multipotent = Multiple related types

Unipotent = Une type

Nullipotent = None

Male gamete — sperm

Shape: Small and streamlined.

Adaptations: Small head, very little cytoplasm, a flagellum for movement, and many mitochondria to provide ATP.

Why? Sperm needs to travel efficiently toward the egg. Being small and streamlined reduces unnecessary mass and allows efficient movement

Female gamete — egg

Shape: Much larger than sperm.

Contains: Lots of cytoplasm, nutrients, and organelles.

Why? The egg needs to provide resources for the early stages of development after fertilisation, so it needs a large volume of cytoplasm.

Red blood cell

Shape: Small and biconcave.

Adaptations: Small, thin/biconcave shape, no nucleus when mature, and packed with haemoglobin.

Why? Its function is to transport oxygen. The biconcave shape increases the surface area relative to volume and shortens the diffusion distance, allowing efficient gas exchange

White blood cell

Shape: Generally larger and more variable in shape than red blood cells.

Why? White blood cells need to move through tissues, change shape, engulf pathogens/particles, and carry out immune functions. 

Flexibility and the ability to change shape are therefore more important than having a regular shape.

Neuron

Shape: Can be extremely long, especially the axon.

Why? Neurons transmit electrical signals over long distances. A long axon allows a signal to travel from one part of the body to another without requiring many separate cells.

Striated muscle cell

Shape: Very long and specialized for contraction.

Adaptations: Often multinucleate, contain many mitochondria, and have specialized contractile structures.

Why? Muscle cells need to generate lots of force and ATP for contraction. Their long shape allows coordinated contraction along the length of the muscle fibre

Overall structure → function relationship

Different specialized cells have different sizes and shapes because their structures are adapted to the specific functions they perform.

What happens when a cell gets bigger?

As cell size increases, SA:V decreases. 

As a cell increases in size, its surface area-to-volume ratio decreases. This reduces the surface area available for exchange relative to the volume requiring nutrients and producing waste, so transport across the membrane may become too slow to meet the cell's metabolic demands.