Human Biology Unit 1 - Scientific method, Cells, Tissues

Chapter 2

What are cells

. The basic structural and functional units of the body, that can perform life’s functions

. Composed of organelles, which maintain homeostasis . Have a large SA:V ratio to allow for nutrient absorption and waste removal

What processes do cells undergo?

. Respiration: breakdown of glucose to release energy for the cell

. Synthesis: building large molecules from smaller ones

. Growth: increase in size or number of cells

Cell Membrane (plasma membrane)

. The outer boundary of the cell that separates cytoplasm inside cell from neighbouring cells + extracellular environment

. controls which substances enter + leave a cell, made up of bilayer of lipids and proteins, contains cholesterol

. differentially permeable and semi permeable (permeable to some substances but not to others)

Cytoplasm

. Thick jelly like fluid within cell membrane that fills the space between cell membrane and organelles

. cytosol + organelles are suspended in, many substances are dissolved in

Cytosol

. The liquid component of the cytoplasm, 75-90% water

. Often has dissolved substances like salts + carbohydrates

. Other insoluble (in water) substances like protein + fats are suspended in

Nucleus

. ovoid/spherical, largest organelle

. contains genetic material (DNA)

. contains nucleolus + nucleoplasm

Function: responsible for maintaining integrity of DNA + controlling cellular activities (metabolism, growth and reproduction) by regulating gene expression

Ribosomes

. very small + spherical

. can be loose in cytoplasm or joined to other organelles (most) like ER (making rough ER)

. connect amino acids together to form proteins (protein synthesis)

Function (do their work in the cytoplasm): convert genetic code into an amino acid sequence, build protein polymers from amino acid monomers

Endoplasmic Reticulum (ER)

. parallel membranes that extend through cytoplasm connecting cell membrane and nuclear membrane

. can be smooth: no ribosomes attached

. can be rough (most): ribosomes attached

. Function: provides a surface for chemical reactions to occur + channels can store and transport materials

. Forms supporting framework of cell

Golgi Apparatus/Body

. flattened membranes stacked one upon the other

Function: . modify proteins and package them in vesicles for secretion from the cell (exocytosis)

—> proteins that are made in ribosomes, pass through the ER to golgi apparatus

—> Edges of golgi apparatus then form vesicles (sacks of liquid containing protein) to secrete the protein out of the cell

Lysosomes

. small spheres that contain enzymes which break down proteins, lipids, nucleic acids and some carbohydrates

Function: break down materials taken into the cell or break down worn out organelles

Vesicle

. small membrane-bound sac that stores and transports materials into, out of or within the cell

Organelle

. a subcellular structure that has one or more specific jobs to perform in the cell

. Suspended in cytoplasm

Mitochondria

. sphere/elongated organelle spread through cytoplasm

. contains circular DNA

. Has double membrane: outer smooth membrane, inner folded membrane (folds = cristae)

. Function: folds allow greater SA for chemical reactions to occur

. releases energy for cell through cellular respiration (occur at cristae, where chemical energy is broken down to form ATP)

Nuclear Pores

. allows molecules to pass through the nucleus

Nuclear Membrane (nuclear envelope)

. separates DNA from the cytoplasm, is double membraned (2 lipid bilayer membranes) + contains pores/gaps

. Controls which substances move through nucleus

Nucleolus

. located inside nucleus

. composed mainly of RNA

. nucleolus and DNA suspended in jelly like nucleoplasm

. involved in manufacture of ribosomes

Centrioles

. pair of cylindrical structures involved in mitosis (reproduction of cell)

. usually located near nucleus

Cilia and Flagella (similarities)

. Fine projections that beat back and forth to either move cell or move substances over the cells surface

Cilia

. lots of short projections that look like hair

. eg: in trachea to move mucus towards the throat

Flagella

. one or two longer projections

. eg: sperm cell tail allows sperm cell to swim

Cytoskeleton

. framework of protein fibres that give cell its shape + assists cell movement

. consists of microtubules, intermediate filaments, and microfilaments

Inclusions

. chemical substances that aren’t part of the cell structure but are found in the cytoplasm

. eg: haemoglobin (RBCs), melanin (skin, hair, eye cells)

Labelled Animal Cell Diagram

Functions of the Cell Membrane (NO?)

. Physical barrier

. Separates cytoplasm from extracellular fluid around it

. Regulation of materials entering + exiting the cell

. Movement of ions and nutrients into cell

. Movement of wastes out of cell

. Release of secretions

Cell Membrane Sensitivity

. membrane detects any changes in the extracellular environment

. eg: an increase of glucose in blood

Cell membrane Support

. membrane is attached to the cytoskeleton which supports the structure of the cell

. cells are attached to one another via the membrane giving rise to tissues

Describe the Cell Membrane Composition

. the design of the composition = the fluid mosaic model

—> as many molecules are located in the cell membrane and are constantly in motion

. Composed of a double layer (bilayer) of phospholipids (are molecules made up of lipids with a phosphate group attached)

—>phospholipid molecules have a hydrophilic + polar head and hydrophobic + non-polar tail (tails are repelled by water and forced to face inwards away from the watery environment, while heads face outwards as they are attracted to the intra+extracellular fluids)

—>hydrophilic molecules can’t cross the hydrophobic tail layer, keeping the 2 (intra + extra) fluids separate

Cell Membrane’s Phospholipid bilayer diagram

Types of Membrane Proteins: 1. Peripheral proteins

. are attached to one side of the membrane only

Types of Membrane Proteins: 2. Integral Proteins

. are located through the membrane

—> many are responsible for transporting ions + small molecules across the membrane

—> these substances are polar (a molecule where electrons aren’t shared equally between atoms, creating a slightly positive end and a slightly negative end on the molecule) or are moving against their concentration gradient (L to H)

Proteins

. large molecules within the cell membrane

. only 2% of membrane are proteins but 55% of cell’s weight is due to the proteins

. Include: receptor proteins, channel proteins, carrier proteins, cell-identity markers

Receptor proteins

. communicate, transmitting info about extracellular stimuli into the cytoplasm

—> certain molecules outside cell bind to receptor proteins which influences changes within cell

—> only one type of receptor protein will bind to one molecule (site specific)

—> Eg: the insulin hormone which is secreted from the pancreas binds to a receptor protein which allows the cell to absorb greater amounts of glucose to aid respiration

—> the limited number of receptor proteins influences the rate of cellular activity

Channel Proteins

. proteins that form pores for specific molecules to pass through

. Transports small, polar, water soluble molecules (Na, Ca, Cl) - large molecules (glucose) can’t pass through

. this (passive) process occurs via facilitated diffusion

. proteins found in the cell membrane that allow substances to pass into and out of the cell

Carrier proteins

. Bind to molecules (eg glucose) and change shape to transport them across the cell membrane and into cell’s cytoplasm

. can be facilitated diffusion (moving molecules w/ concentration gradient) + active transport (against gradient)

—> protein changes its own shape

—> are specific

—> the number of carrier proteins limits the intake of molecules into the cell

—> substances such as hormones will trigger carrier proteins binding to molecules

Cell-Identity Markers

. serve as recognition markers for the body’s immune system

. the body’s immune system recognises these cells and thus these cells won’t be destroyed

Cell Membrane Diagram

Cell Membrane: Semi/selective/differentially permeability

. ability to allow only certain molecules in or out of the cell

. cells must exchange materials such as nutrients + gases with their environment by allowing them to pass through their membrane

—> lipid bilayer permeable to: few small uncharged molecules (O2, CO2)

—>Impermeable to: large, polar/ionic compounds

What 3 main components make up the cell membrane

1. Phospholipid bilayer

2. Cholesterol

3. Membrane proteins

Cholesterol Molecules in the Cell Membrane

. wedged between the phospholipid molecules

. provide flexibility + improve the structural integrity of the membrane, helping the membrane keep its shape

Function 1 of the Cell Membrane (YES?)

Acts as a physical barrier:

. separates intracellular fluid (cytoplasm) from extracellular fluid

Function 2 of Cell Membrane

Regulates the passage of materials:

. controls movement of materials in + out of cell

Function 3 of Cell Membrane

Able to sense changes:

. cell membrane is first part of cell affected by any changes in extracellular fluid, containing receptor proteins that can respond to changes in the extracellular fluid very quickly

Function 4 of Cell membrane

Helps to support the cell:

. contains structural molecules that give cell shape + allow it to join with other cells

. internal part of the membrane is attached to the microfilaments of cell’s cytoskeleton, giving support to the whole cell

1. Simple diffusion

. movement of certain substances directly through the lipid bilayer (alcohol, oxygen, CO2)

. passive process, no energy required

. substances move from high concentration to low concentration

—> eg: oxygen into cells, carbon dioxide out of cells

What does the rate of diffusion depend on?

1. The concentration gradient: greater difference in concentration between the 2 regions of the substance, the greater the rate of diffusion

2. The size and nature of the diffusing molecule: smaller molecules diffuse faster than large ones

3. The distance over which diffusion takes place: shoter=greater rate of diffusion

4. The area over which diffusion takes place: larger surface area=greater rate of diffusion

2. Facilitated Diffusion

. type of passive transport in which the molecules move from the region of higher concentration to the region of lower concentration assisted by a channel or carrier protein

—> as some molecules are too large to diffuse through the cell membrane on their own (amino acids + glucose), the molecule uses a protein within the cell membrane + is moved into or out of the cell

. rate of facilitated diffusion is dependent on the amount of proteins being used

. is specific

3. Active Transport

. the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration (against the concentration gradient)

. carrier proteins used to transfer molecules from outside of cell into cell

. cell must use energy (ATP)

4. Vesicular Transport

. a cellular process responsible for moving (large) molecules across and within cells using membrane-bound sacs called vesicles

. an active process

. maintains homeostasis and communication between cells by the release of neurotransmitters in nerve cells

Vesicular transport: Endocytosis

. the movement of molecules into the cell via vesicular transport

. the membrane surrounds the substance + then pinches off to form a vesicle which then is suspended in cytoplasm

. eg: engulfing bacteria by white blood cells

Endocytosis: Pinocytosis

. entering of liquid substances

. The process by which a cell takes in small molecules and fluids from the extracellular fluid into the cytoplasm

—> when the cell takes in the fluid, it’s stored in a tiny vesicle provided by the cell membrane

Endocytosis: Phagocytosis

. entering of solid substances

. Process by which phagocytes (living cells) ingest other cells or particles, including foreign substances, microorganisms and apoptotic cells

—> these phagocytes rise the membrane to an internal compartment called the phagosome

Vesicular Transport: Exocytosis

. the movement of substances out of the cell via vesicles

—> substances move from the golgi towards cell membrane via a vesicle, then fuses with cell membrane and its contents escapes into the extracellular environment

Active vs Passive Transport

Active: requires energy (ATP) to move molecules across a cell membrane against their concentration gradient (L to H)

Passive: doesn’t require energy and moves molecules down their concentration gradient (H to L)

Tissue types: Muscular tissue

. contractile tissue

3 types:

1. Skeletal muscle: tissue that’s attached to bones, voluntary, allows for movement

2. Smooth muscle: supports internal organs, involuntary (moving substances down our pipes), found in the walls of hollow organs (intestines) and passageways (veins)

3. Cardiac muscle: makes up the walls of heart, involuntary

Tissue Types: Epithelial Tissue (MORE NEEDED?)

. bricks on a wall appearance

. lines surface

. eg: skin, the lining of GI tract

Tissue Types: Connective Tissue

. provides support and structure

. cells are spread far apart in an extracellular matrix

. eg: bone, cartilage, blood

Tissue types: Nervous Tissue

. composed of neurons

. neurons carry information to parts of the body by electrochemical messages known as action potentials

The 4 Tissue Types Appearance

Osmosis

. the movement of water from an area of low solute (high water) concentration to an area of high solute (low water) concentration, through a selectively permeable membrane

—> special type of diffusion involving water

—> occurs via channel proteins in cell membrane (aquaporins)

—> from dilute to concentrated solutions

—> passive process, no energy required

Aquaporins

. integral membrane proteins, which are water-selective, that facilitate the movement of water by osmosis

. water channels

. water molecules can travel through aquaporins + semi-permeable membrane

—> water moves through cells most rapidly in tissues that have aqauporins

Osmotic pressure

. the pressure created by water moving across the membrane due to osmosis, to create equilibrium

—> the higher solutes in solution = higher osmotic pressure

—> pressure needs to be applied to halt osmosis

Isotonic solution

. a solution that has the same solute concentration as another solution

. no net movement of water particles + overall concentration on both sides of cell membrane remains constant

—> rate of water movement in and out is equal

—> cell = normal size

Hypertonic solution

. a solution that has a higher solute concentration (lower water) than another solution

On the outside: concentrated solutes outside

—> water particles will move out of cell, causing crenation + cell shrinking

Hypotonic solution

. a solution that has a lower solute concentration (higher water) than another solution

On the outside: dilute solutes outside

—> water particles will move into cell, causing cell to expand (swell) and eventually lyse (burst)

Solvent

. a substance, often water, in which a solute is dissolved

Solute

. a substance that can be dissolved in a solvent

Tonicity

. the ability of an extracellular solution to make water move into or out of a cell by osmosis

. a solution’s tonicity is related to its osmolarity

Osmolarity

. the total concentration of all solutes in the solution

. solution with low osmolarity has fewer solute particles per litre of solution

. solution with high osmolarity has more solute particles per litre of solution

—> when solutions of different osmolarities separated by membrane permeable to water, but not to solute, water move from side with lower osmolarity to higher

Hypotonic solution osmolarity

. extracellular fluid has lower osmolarity than the fluid inside the cell

. net flow of water will be into the cell

. solute concentration inside cell = higher

Hypertonic solution osmolarity

. extracellular fluid has higher osmolarity than cell fluid

. water diffuses out of cell

isotonic solution osmolarity

. extracellular is the same osmolarity as the cell

. no net movement of water in and out, amount transported into cell = amount transported out

Surface Area to Volume Ratio for Diffusion Efficiency

. smaller cells have a larger SA:V ratio, which allows faster diffusion

. as a cell grows, its volume increases faster than its SA, reducing efficiency

Why are cells small?

. a high SA:V ratio ensures efficient exchange of nutrients and waste

. large cells struggle to get enough oxygen + nutrients

. cells divide instead of growing too large to maintain efficiency

How do you increase reliability

. repeat trials

How do you increase validity

. control ..

How do you increase accuracy

. use right equipment, use equipment correctly

Examples of Endocytosis

1. Phagocytosis: White blood cells engulfing bacteria

2. Pinocytosis: absorption of nutrients in the small intestine

Examples of Exocytosis

1. Nerve signal transmission/neurotransmitter release

2. Hormone (insulin) secretion

3. Mucus and Enzyme secretion: stomach cells secrete digestive enzymes to break down food