Bio Unit 1 chapter 1

Cell

The basic structural unit of all life forms on Earth

Organelle

A specialised structure or compartment within a cell that has a specific function.

Structure VS Function

• Structure: What does it look like? What is it made from?

• Function: What does it do? What is its job?

Characteristics of living things

MRS GREEN

Movement

Respiration

Sensitivity

Growth

Reproduction

Excretion

Equilibrium 

Nutrition

Cell Theory

• The cell is the smallest unit of life (nothing smaller than a cell is considered to be living – e.g. viruses are not alive)

• All living things are composed of cells (or cellular products) – i.e. living organisms may be unicellular or multicellular

• Cells arise from pre-existing cells – life cannot spontaneously generate

Organism

Any living thing that performs all the functions of life and can operate as an independent entity.

Prokaryotic cells

• No membrane-bound organelles

• No nucleus (DNA in nucleoid region).

• Unicellular

• Tend to be smaller and simpler than eukaryotic cells

• Found in bacteria and archaea

Eukaryotes

• Have membrane-bound organelles.

• Have a nucleus containing DNA.

• More complex

• Tend to be larger than prokaryotic cells

• Unicellular or multicellular

• Found in animals, plants, protists and fungi

Similarities between eukaryotic cells and prokaryotic cells

• Both can be unicellular

• Contain plasma membrane, cytoplasm and ribosomes

• Use DNA to store genetic material

Plasma membrane

• All cells are surrounded by it

• Selectively permeable barrier.

• Separates the intracellular environment with the extracellular environment.

• Made of a phospholipid bilayer

The 6 kingdoms of life

Bacteria, Archaea, Protists, Fungi, Plants, Animals

What is SA:V?

• Ratio of surface area (2D) to volume (3D)

• Describes how much membrane is available to service cell contents

How does size affect SA:V?

• As cell size increases, the volume increases more than surface area.

• The inside of the cell becomes bigger than the membrane can efficiently support.

• Result: SA:V decreases

• Cells with a larger surface-area-to-volume ratio can obtain nutrients and remove wastes more efficiently.

Why is a high SA:V important?

Faster exchange of:

• Nutrients

• Gases

• Wastes

Therefore, cells with high SA:V are more efficient

How does shape affect SA:V?

• Shape can increase SA without much increase in volume

• Sphere = lowest SA:V

• Long, thin or flat cells = higher SA:V

• Cells have adaptations to maximise SA:V

What is compartmentalisation and why is it important in eukaryotic cells?

• the use of internal membranes to create specialized, enclosed regions (organelles) within a eukaryotic cell.

This allows:

• Different chemical reactions to occur simultaneously

• Greater efficiency

• Increased internal surface area

• Enables cell specialisation and complex multicellular life.

How does the nucleus coordinate cell activities?

Contains DNA, organised into chromosomes.
DNA codes for proteins.
By controlling which proteins are made, the nucleus:

• Regulates cell structure

• Controls metabolic processes

• Enables cell specialisation

Surrounded by a porous nuclear membrane.

What is the function of mitochondria?

Site of aerobic cellular respiration.
Break down glucose using oxygen.
Produce:

• Carbon dioxide

• Water

• ATP (energy storage molecule)

  • ATP provides energy for cellular processes.

• Folded inner membrane (cristae) increases surface area for ATP production.

How does structure relate to function in organelles?

• Membranes create specialised environments.

• Increased surface area improves efficiency (e.g., cristae).

• DNA in the nucleus allows regulation of protein synthesis.

• Organelles work together to maintain cellular function.

Cytosol

The part of the cytoplasm containing highly organized fluid material with dissolved substances; excluding the organelles

Chromosome

A structure made of a DNA molecule

Nuclear membrane

The membrane surrounding the nucleus

Nucleolus

• small structure found in nucleus

• A site for assembling protein and RNA that will later form ribosomes

Ribonucleic acid (RNA)

The single-stranded nucleic acid that functions in transcribing and translating information from DNA into proteins

Cellular respiration

Cellular chemical equation

• Inputs: Glucose + Oxygen

• Outputs: Carbon Dioxide + Water + Energy (ATP)

• The energy released is used to convert ADP and inorganic phosphate into ATP

Mitochondrion (singular)

• Primary method to supply ATP (energy) to the cell to allow it to function.

• They are known as sites of aerobic cellular respiration.

• Contains their own circular DNA and ribosomes.

• Has a highly folded inner membrane surrounded by a second membrane

Nucleus

• Coordinates all activities in a cell.

• DNA (deoxyribonucleic acid) main molecule found within the nucleus.

• DNA compacted and tightened into chromosomes that code for production of proteins and contains ‘blueprint’ of the organism. 

• These proteins carry out a variety of activities within the cell.

Cytoplasm and cytosol

• Cytosol is the internal area or ‘free’ space of a cell. 

• Chemical reactions are carried out in the cytoplasm.

• Cytoplasm contains a fluid part called the cytosol which does not contain organelles

• Cytoplasm = cytosol + all cell organelles dispersed through it (excluding nucleus)

Ribosomes

• Ribosomes make proteins by putting together small building blocks of amino acids. 

• Proteins are needed for cell growth, repair and general cell functioning

• Float freely in the cytosol or attached to the rough endoplasmic reticulum.

Endoplasmic Reticulum

• Is made of membrane-bound flattened sacs and tubules

• Attached to the nucleus

• Main jobs:

  • Transport the proteins made at the ribosomes around the cell

  • Transport proteins from one cell to another

• There are 2 types of ER 

  • Smooth ER = without ribosomes

  • Rough ER = with ribosomes attached 

• The ER is basically a highway that connects and delivers proteins to different parts of the cell city
  

Rough Endoplasmic Reticulum

• An interconnecting system of flattened membrane sacs coated with ribosomes (rough).

• Synthesises and modifies proteins.

• An intracellular transport system.

• Positioned close to the nucleus

Golgi apparatus

• Stacks of flattened sacs.

• Sites of protein sorting, packaging and modification. 

• Proteins are then used in the cell or exported from the cell in vesicles that move to the plasma membrane, where they join to the membrane and discharge their contents to the outside of the cell.

Lysosome

• Membrane-bound vesicle.

• Contains digestive enzymes.

• Breaks down cell waste and toxins, acting like a garbage disposal.

Cytoskeleton

• Large network of protein filaments starting at nucleus extend towards plasma membrane.

• Maintaining shape and transporting vesicles around the cell.

Components of the cytoskeleton

Plasma membrane, endoplasmic reticulum, microtube, mitochondria, microfilaments

Vacuole

• Membrane-bound sac.

• Used for water and solute storage.

• Maintains plant cell structure.

• Found in plant and fungal cells. Some protists, animal, and bacterial cells.

• Plant cells usually have one large vacuole

• Animal cells have multiple small vacuoles

Cell Wall

• Sturdy border outside the plasma membrane.

• Provides strength and structure to plant, bacterial and fungal cells. Some protists.

Chloroplast

• Double-membrane-bound organelle.

• Contains flattened, fluid-filled sacs.

• Site of photosynthesis.

• Contains its own circular DNA and ribosomes.

• Found in plant and algae cells.

Photosynthesis

The process by which plants convert light energy into chemical energy (sugars) to fuel cellular activities

Chlorophyll

• A green pigment contained in thylakoid membranes

• It absorbs light to energise reactions in the chemical reaction of photosynthesis

• Glucose is then used in cellular respiration to:

  • Build cell walls

  • Carry out metabolic (chemical) reactions

What is the primary role of the plasma membrane?

• Forms the boundary between the internal and external environment of the cell, the cytoplasm and its environment

• Composed of a double layer of phospholipid molecules, each of which can be represented by a head and two tails

• Found in both eukaryotes and prokaryotes.

• Selectively permeable- allows some substances to pass across it but not others

Cell Wall vs. Membrane

Cell Wall: (Plants, fungi, bacteria) is fully permeable and provides structural support.

Plasma Membrane: (All cells) is selectively permeable and regulates transport.

The Phospholipid Molecule

• Phosphate Head: Polar and hydrophilic ("water-loving"). It faces the watery environments inside and outside the cell.

• Fatty Acid Tails: Non-polar and hydrophobic ("water-fearing"). They face inwards, away from water.

• The Bilayer: These properties force phospholipids to form a double layer (bilayer) where tails are shielded in the middle.

Why is the membrane described as a "Fluid Mosaic"?

Fluid: The phospholipids are not bonded together; they move laterally (sideways) like a liquid. This allows the cell to change shape and form vesicles.

Mosaic: A variety of different proteins are embedded or attached to the bilayer, creating a "pattern" or mosaic.

Transport (Transmembrane)Proteins:

Regulate the movement of substances (like ions or glucose) across the membrane. 

They span the entire width of the phospholipid bilayer.

Receptor Proteins:

They are transmembrane proteins that span the entire bilayer. 

Have specific binding sites for signaling molecules (like hormones). 

Essential for cellular communication, allowing the cell to “receive”messages

Recognition Proteins (Glycoproteins)

Act as markers to identify "self" vs "non-self" (immune function). 

A transmembrane protein with a branched carbohydrate chain attached to the extracellular surface.

Adhesion Proteins

Link cells together to form tissues.

Lipid

A diverse group of organic, non-polar compounds composed mainly of carbon, hydrogen, and oxygen that are largely insoluble in water

Hydrophilic

• H2O attracted

• Polar molecules (charged)

• May need assistance to cross the membrane through a protein channel

• E.g. glucose, amino acids, ions

Hydrophobic

• H2O repelling

• Non-polar molecules (no charge)

• Can easily cross the plasma membrane

• E.g. alcohol, lipids, gases

Cholesterol

• Type of lipid

• Embedded in between the fatty acid tails.

• Acts as a buffer against temperature fluctuations to keep the membrane stable.

• At high temperatures, it reduces the motion of the phospholipid tails, decreasing fluidity so the membrane doesn't become too liquid.

• At low temperatures, it prevents phospholipids from clustering too closely, increasing fluidity so the membrane doesn't freeze or become too solid.

• Found in animal cells

Transmembrane

Proteins that spans both sides of the membrane

Integral

Proteins embedded within the plasma membrane

Peripheral

Proteins attached to the membrane but are not embedded in it.

Glycolipid

Carbohydrate chain attached to a lipid

Extracellular

The environment outside the cell.

Intracellular

The environment inside the cell (cytoplasm/cytosol).

Permeable

allows liquids or gases to pass through it easily

Selectively Permeable

only allows certain substances to pass through while blocking others

Diffusion

The movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached.

The bigger the difference in concentration, the faster it will move

• High to low concentration

• No protein required

• No energy required

Equilibrium

The point where particles are distributed evenly and move at equal rates in all directions.

Facilitated Diffusion

• Charged particles (ions) and large molecules (like glucose) are repelled by the hydrophobic lipid tails and need help

• The "Helpers": Specific transport proteins assist these molecules:

  • Channel Proteins: Form narrow, water-filled "tunnels" for water-soluble substances.

  • Carrier Proteins: Bind to a specific molecule(e.g. glucose), change shape, and release it on the other side of the molecule

• Polar/hydrophilic molecules transported

• Large molecules

• High to low concentration

• Protein required

• No energy required

Simple Diffusion

Small, uncharged, or hydrophobic(oxygen, co2) molecules slip directly between phospholipids.

• High to low concentration

• No protein required

• No energy required

What are the factors of the rate of diffusion

The process is faster when there is a 

• greater concentration gradient 

• Increase in temperature

Osmosis

Diffusion of water molecules from an area of high H2O concentration to an area of low H2O concentration through a semi-permeable membrane without the use of energy.

• Direction: from hypotonic to hypertonic solution

• Protein is sometimes required

• No energy required

Tonicity

A measure of the relative concentration of solutes on either side of a semipermeable membrane.

Described as hypertonic, hypotonic, or isotonic

Hypertonic

A solution with a higher solute concentration than the cell (water leaves)

Hypotonic

A solution with a lower solute concentration than the cell (water enters).

Isotonic

A solution with the same solute concentration as the cell (no net water movement).

Osmosis in Animal Cells (red blood cells)

• In a hypotonic solution (like pure water), they will swell and burst.

• lysis occurs

• it refers to the breakdown, destruction, or rupturing of the outer plasma membrane of a cell, resulting in the release of its internal contents and the death of the cell.

Osmosis in Plant Cells

They do not burst because they have a tough, external cell wall.

When water enters, the vacuole swells and pushes against the cell wall, making the cell turgid (firm).

Solute

The substance that is dissolved in a liquid (e.g., salt or sugar).

Passive Transport

Movement across a membrane that does not require energy(ATP)

• Moves substances down the concentration gradient (from High to Low).

• Simple diffusion, facilitated diffusion, and osmosis

ATP (Adenosine Triphosphate)

The main cellular source of chemical energy used to power active transport.

Carrier Protein

A protein that changes shape to move molecules across the membrane

• used in facilitated diffusion & active transport

Channel Protein

 A protein that forms a watery "tunnel" for specific ions; used only in facilitated diffusion.

Concentration Gradient

The difference in particle concentration between two regions. 

Active Transport

The movement of particles up a concentration gradient (from low concentration to high concentration).

• Requires ATP to power the carrier protein to force the molecule against the concentration gradient

• Counteracts the natural push of diffusion.

• Uses specific carrier proteins in the plasma membrane that work as "one-way valves."

• Individual small molecules/ions (like Glucose or Na+)

Endocytosis

An active process where the plasma membrane surrounds a large particle or liquid to form a vesicle, bringing it into the cell.

• 2 types: phagocytosis and pinocytosis

• Requires ATP to change the shape of the membrane and move the vesicles.

Phagocytosis

• A specific form of endocytosis-"cell eating."

• It is the process by which a cell engulfs large, solid particles or even entire foreign cells (like bacteria) from the external environment.

• (e.g., an Amoeba eating prey or a human white blood cell engulfing bacteria).

Pinocytosis

• A specific form of endocytosis (bulk transport) known as "cell drinking."

• It is the process by which a cell takes in extracellular fluid and the dissolved substances (solutes) it contains.

Exocytosis

The process by which large molecules held in vesicles are transported out of the cell.

• Mechanism: A vesicle moves to the plasma membrane, fuses with it, and releases its contents to the external environment.

• The Golgi apparatus is responsible for packaging these substances into vesicles for export.

Vesicle

A small, membrane-bound sac used to transport, store, or digest substances.

Metabolism

The total sum of all chemical reactions occurring within a cell.

Bulk Transport

(Endocytosis/Exocytosis) is for large volumes or large particles moving via membrane folding and vesicles.