Biology part.2

Plasma Membrane

A phospholipid bilayer with proteins that separates the inside of the cell from its surrounding environment.

What is one main job of the plasma membrane?

It controls which substances enter and leave the cell.

Why must the plasma membrane be flexible?

Flexibility allows cells such as red and white blood cells to change shape when moving through narrow spaces.

What do markers on the plasma membrane do?

They allow cells to recognize one another.

Membrane Receptors

Receptors are specific attachment sites on the plasma membrane that bind particular substances.

Why are membrane receptors specific?

Each receptor has a structure that allows it to bind with a particular substance.

Fluid Mosaic Model

The fluid mosaic model describes the membrane as a flexible mixture of phospholipids, cholesterol, proteins, and carbohydrates whose components can move.

Why is the plasma membrane called fluid?

Its phospholipids and embedded proteins can move laterally within the membrane.

Phospholipid Bilayer

The phospholipid bilayer is two layers of phospholipids that form the main structure of the plasma membrane.

Which parts of phospholipids face water?

The polar hydrophilic ends face the watery environments inside and outside the cell.

Which parts of phospholipids face inward?

The hydrophobic fatty acid tails face inward away from water.

Hydrophilic

Hydrophilic means attracted to or able to interact with water.

Hydrophobic

Hydrophobic means not attracted to water.

What does cholesterol do in an animal cell membrane?

Cholesterol helps regulate the fluidity of the plasma membrane.

Integral Proteins

Integral proteins are embedded in the plasma membrane and may act as channels or pumps.

Peripheral Proteins

Peripheral proteins are attached to the inner or outer surface of the plasma membrane.

What can membrane proteins do?

Membrane proteins can transport materials, act as enzymes, provide structural attachment, or help cells recognize substances.

Where are membrane carbohydrates located?

Membrane carbohydrates are found on the exterior surface of cells.

Glycoprotein

A glycoprotein forms when a carbohydrate is attached to a protein.

Glycolipid

A glycolipid forms when a carbohydrate is attached to a lipid.

What is an important function of membrane carbohydrates?

Membrane carbohydrates help cells recognize one another.

Selectively Permeable

A selectively permeable membrane allows some substances to pass through while preventing others from passing.

Passive Transport

Passive transport moves substances without requiring the cell to use energy.

What direction do substances move during passive transport?

Substances generally move from an area of higher concentration to an area of lower concentration.

Concentration Gradient

A concentration gradient is a difference in the concentration of a substance across an area.

Diffusion

Diffusion is the passive movement of a substance from high concentration to low concentration.

Does diffusion require cellular energy?

Diffusion does not require the cell to expend energy.

When does diffusion reach equilibrium?

Equilibrium is reached when the substance becomes evenly distributed across the available space.

How does a larger concentration gradient affect diffusion?

A larger difference in concentration causes diffusion to occur more rapidly.

How does molecular mass affect diffusion?

More massive molecules generally diffuse more slowly than smaller molecules.

How does temperature affect diffusion?

Higher temperatures increase molecular movement and therefore increase the rate of diffusion.

How does solvent density affect diffusion?

Increasing solvent density decreases the rate of diffusion.

What molecules can easily cross the hydrophobic membrane core?

Lipid-soluble and small uncharged molecules can easily pass through the hydrophobic membrane core.

Can oxygen and carbon dioxide cross the membrane by simple diffusion?

Oxygen and carbon dioxide are uncharged molecules that can cross by simple diffusion.

Why do ions have difficulty crossing the plasma membrane?

Their electrical charges prevent them from easily passing through the hydrophobic lipid core.

Facilitated Transport

Facilitated transport moves substances from high to low concentration through membrane proteins without using cellular energy.

Does facilitated diffusion require energy?

Facilitated diffusion uses transport proteins but does not require cellular energy.

Why is facilitated transport needed?

It allows substances that cannot easily cross the lipid membrane to move through transport proteins.

Simple Diffusion vs Facilitated Diffusion

Both move substances from high to low concentration without energy, but facilitated diffusion uses membrane proteins.

Transport Proteins

Transport proteins act as channels or carriers that help specific substances cross the plasma membrane.

Osmosis

Osmosis is the movement of water across a semipermeable membrane from high water concentration to low water concentration.

What substance moves during osmosis?

Osmosis specifically describes the movement of water.

Solute

A solute is a substance dissolved in another substance to form a solution.

Tonicity

Tonicity describes the amount of solute in a solution.

Osmolarity

Osmolarity is the total amount of solutes dissolved in a specific amount of solution.

Hypotonic Solution

A hypotonic solution has a lower solute concentration outside the cell than inside the cell.

Which way does water move in a hypotonic solution?

Water moves into the cell when the surrounding solution is hypotonic.

What can happen to an animal cell in a hypotonic solution?

An animal cell can swell and burst as water enters it.

Hypertonic Solution

A hypertonic solution has a higher solute concentration outside the cell than inside the cell.

Which way does water move in a hypertonic solution?

Water moves out of the cell when the surrounding solution is hypertonic.

What can happen to an animal cell in a hypertonic solution?

An animal cell can shrivel as water leaves it.

Isotonic Solution

An isotonic solution has the same osmolarity as the fluid inside the cell.

What happens to water in an isotonic solution?

There is no net movement of water into or out of the cell.

Hypotonic vs Hypertonic

Hypotonic solutions cause water to enter cells while hypertonic solutions cause water to leave cells.

Why don't plant cells normally burst when water enters them?

Their rigid cell walls limit expansion and prevent the cells from lysing.

Turgor Pressure

Turgor pressure is pressure produced when water entering a plant cell pushes against its cell wall.

What happens when plant cells lose turgor pressure?

The plant loses support and wilts.

Active Transport

Active transport uses cellular energy to move substances across a membrane.

What energy source is usually used for active transport?

Active transport usually uses energy from ATP.

What direction can active transport move substances?

Active transport can move substances against their concentration gradient from lower to higher concentration.

Passive vs Active Transport

Passive transport does not require energy while active transport requires cellular energy.

Electrochemical Gradient

An electrochemical gradient combines differences in ion concentration with differences in electrical charge across a membrane.

Why must cells use energy to move substances against a gradient?

Moving against a concentration or electrochemical gradient requires energy from ATP.

Sodium-Potassium Pump

The sodium-potassium pump uses energy to move potassium into the cell and sodium out of the cell.

Primary Active Transport

Primary active transport directly uses ATP to move substances across a membrane.

Secondary Active Transport

Secondary active transport uses energy stored in an electrochemical gradient created by primary active transport.

Endocytosis

Endocytosis is active transport that brings large particles or substances into a cell using the plasma membrane.

What happens to the membrane during endocytosis?

The plasma membrane folds inward around material and pinches off to form a membrane-bound compartment.

Phagocytosis

Phagocytosis is a type of endocytosis in which a cell takes in large particles such as cells or cell fragments.

Pinocytosis

Pinocytosis is a type of endocytosis that takes in extracellular fluid and dissolved solutes.

Receptor-Mediated Endocytosis

Receptor-mediated endocytosis uses specific membrane receptors to bring particular substances into a cell.

Exocytosis

Exocytosis releases material when a membrane-bound vesicle fuses with the plasma membrane.

Endocytosis vs Exocytosis

Endocytosis brings material into the cell while exocytosis releases material from the cell.

Cell Wall

The cell wall is a rigid covering that protects the cell, provides structural support, and gives the cell shape.

Central Vacuole

The central vacuole is a large plant organelle used for storage, water retention, and macromolecule breakdown.

Chloroplast

A chloroplast is the organelle in which photosynthesis occurs.

Cytoplasm

Cytoplasm is the region between the plasma membrane and nuclear envelope containing organelles, cytosol, cytoskeleton, and chemicals.

Cytosol

Cytosol is the gel-like material in which cellular structures are suspended.

Cytoskeleton

The cytoskeleton is a network of protein fibers that supports cell shape and helps organize and move structures within the cell.

Nucleus

The nucleus houses the cell's DNA and directs the synthesis of ribosomes and proteins.

Nucleolus

The nucleolus is the region inside the nucleus responsible for assembling ribosomal subunits.

Ribosome

A ribosome is a cellular structure that carries out protein synthesis.

Endoplasmic Reticulum

The endoplasmic reticulum is a network of membranes that modifies proteins and synthesizes lipids.

Rough Endoplasmic Reticulum

The rough ER is covered with ribosomes and participates in protein modification.

Why does rough ER look rough?

Rough ER looks rough because ribosomes are attached to its cytoplasmic surface.

Ribosome vs Rough ER

Ribosomes synthesize proteins while the rough ER helps modify proteins.

Smooth Endoplasmic Reticulum

Smooth ER synthesizes carbohydrates, lipids, and steroid hormones while also detoxifying chemicals and storing calcium ions.

RER vs SER

RER has attached ribosomes and modifies proteins while SER has few or no ribosomes and performs functions including lipid synthesis and detoxification.

Golgi Apparatus

The Golgi apparatus sorts, tags, and packages proteins and lipids for distribution.

Lysosome

A lysosome contains digestive components that break down biological molecules and worn-out organelles.

Mitochondria

Mitochondria carry out cellular respiration to produce ATP.

Peroxisome

A peroxisome oxidizes fatty acids and amino acids and detoxifies many poisons.

Vesicle

A vesicle is a small membrane-bound sac used for cellular storage and transport.

Vacuole

A vacuole is a membrane-bound sac used for cellular storage and transport that is generally larger than a vesicle.

Prokaryotic Cell

A prokaryotic cell lacks a nucleus and other membrane-bound organelles.

Eukaryotic Cell

A eukaryotic cell contains a membrane-bound nucleus and other membrane-bound compartments.

Bioenergetics

Bioenergetics is the concept of energy flow through living systems.

Metabolism

Metabolism includes all chemical reactions occurring inside cells, including reactions that use or release energy.

Metabolic Pathway

A metabolic pathway is a series of chemical reactions that modifies a starting molecule step-by-step into a final product.

Anabolic Pathway

An anabolic pathway requires energy to build larger complex molecules from simpler molecules.