Slides__A2.2_Cell_Structure__AHL_

Cell Theory

States that all living things are composed of cells, cells are the basic units of life, and all cells arise from pre-existing cells.

What are the three main tenets of the Cell Theory?

1. All living things are composed of cells. 2. Cells are the basic units of life. 3. All cells arise from pre-existing cells.

Prokaryotic cells lack a true and other membrane-bound organelles.

nucleus

Eukaryotic cell

A cell that contains a true nucleus and other membrane-bound organelles.

Prokaryotic cell

A simple cell lacking a nucleus and other membrane-bound organelles.

How do prokaryotic cells divide?

Through binary fission.

Nucleus

Contains the cell's genetic material (DNA) organized into chromosomes and controls cell activities.

The nuclear envelope is a double membrane that encloses the .

nucleus

Nucleolus

A dense structure within the nucleus responsible for ribosome synthesis.

Mitochondrion (plural: Mitochondria)

Site of aerobic respiration and ATP production. Known as the 'powerhouse' of the cell.

What are the folds of the inner mitochondrial membrane called?

Cristae, which increase the surface area for cellular respiration.

The fluid-filled space within the mitochondrion, enclosed by the inner membrane, is called the .

matrix

Chloroplast

Site of photosynthesis in plant cells and some protists. Contains chlorophyll.

What are the stacks of thylakoids within a chloroplast called?

Grana (singular: granum).

The fluid-filled space surrounding the grana within a chloroplast is called the .

stroma

Rough Endoplasmic Reticulum (RER)

Network of membranes studded with ribosomes, involved in synthesis, folding, modification, and transport of proteins destined for secretion or insertion into membranes.

Smooth Endoplasmic Reticulum (SER)

Network of membranes without ribosomes, involved in lipid synthesis, detoxification of drugs and poisons, and storage of calcium ions.

What is the primary function of ribosomes attached to the RER?

To synthesize proteins that will be secreted from the cell, incorporated into membranes, or delivered to other organelles like lysosomes.

Golgi apparatus (or Golgi complex/body)

Stack of flattened membrane-bound sacs (cisternae) that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

Outline the path of a secreted protein from synthesis to secretion.

Ribosomes on RER
→ RER lumen
→ transport vesicles
→ Golgi apparatus (cis face to trans face)
→ secretory vesicles
→ cell membrane (exocytosis).

Lysosome

A membrane-bound sac containing hydrolytic enzymes, responsible for breaking down waste materials, cellular debris, and foreign invaders (e.g., bacteria).

Lysosomes are often referred to as the "suicide bags" of the cell due to their role in , the self-digestion of a cell.

autolysis

Peroxisome

Contains enzymes like catalase, involved in metabolic processes like fatty acid breakdown and detoxification of harmful substances, producing hydrogen peroxide as a byproduct.

Vacuole

A membrane-bound sac used for storage of water, nutrients, waste products, and pigments. Especially large in plant cells, where it maintains turgor pressure.

What is the specialized membrane enclosing the large central vacuole in plant cells?

Tonoplast.

Ribosome

A complex of ribosomal RNA (rRNA) and protein that carries out protein synthesis (translation).

Eukaryotic ribosomes are S, while prokaryotic ribosomes are S.

80, 70

Cytoskeleton

A network of protein filaments and tubules in the cytoplasm, providing structural support, maintaining cell shape, and enabling cell movement and transport of organelles.

Name the three main types of protein filaments that make up the cytoskeleton.

Microtubules, microfilaments (actin filaments), and intermediate filaments.

Centrioles

Cylindrical structures found in most animal cells, involved in cell division and the formation of cilia and flagella. (Part of the centrosome).

Cell wall

A rigid layer outside the cell membrane of plant cells, fungi, bacteria, and some protists, providing structural support, protection, and preventing excessive water uptake.

What is the primary component of the plant cell wall?

Cellulose.

Cell membrane (Plasma membrane)

A selectively permeable barrier surrounding the cytoplasm of a cell, composed of a phospholipid bilayer with embedded proteins, regulating the passage of substances into and out of the cell.

The current model of the cell membrane is known as the model, describing it as a dynamic, fluid structure.

fluid mosaic

What are the two main types of molecules that make up the majority of the cell membrane?

Phospholipids and proteins.

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. A passive process.

Facilitated diffusion

The passive movement of specific molecules across a cell membrane through protein channels or carriers, down their concentration gradient, without the expenditure of ATP.

Osmosis

The net movement of water molecules from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration) across a partially permeable membrane.

Describe what happens to an animal cell when placed in a hypotonic solution.

Water will move into the cell by osmosis, causing it to swell and potentially burst (lysis), as it lacks a cell wall.

Describe what happens to a plant cell when placed in a hypertonic solution.

Water will move out of the cell by osmosis, causing the protoplast to shrink and pull away from the cell wall (plasmolysis). The cell wall prevents bursting.

Active transport

The movement of substances across a cell membrane against their concentration gradient, requiring energy (ATP) and specific protein pumps.

The sodium-potassium pump is an example of transport, maintaining concentration gradients essential for nerve impulses.

active

Endocytosis

The process by which cells take in substances from their external environment by engulfing them in a portion of the cell membrane, forming a vesicle.

What are the two main types of endocytosis?

Phagocytosis (cell eating, engulfing solids) and Pinocytosis (cell drinking, engulfing liquids/solutes).

Exocytosis

The process by which cells release substances from internal vesicles to the outside of the cell by fusing the vesicle membrane with the cell membrane.

Give an example of a substance released from a cell by exocytosis.

Hormones, neurotransmitters, digestive enzymes, waste products.

Magnification

The number of times larger an image appears compared to the actual size of the object.

Resolution

The ability of a microscope to distinguish between two separate points or objects, showing fine detail.

Electron microscopes have higher than light microscopes, allowing for visualization of internal ultrastructure.

resolution

Why are electron micrographs typically black and white?

Electron microscopes use a beam of electrons instead of light, and the images are digitally generated based on electron diffraction and then often artificially colored.

Ultrastructure

The fine structure of a cell or tissue, especially as revealed by electron microscopy.

Stem cell

An undifferentiated cell that has the ability to self-renew (divide repeatedly) and to differentiate into various specialized cell types.

What is the difference between totipotent, pluripotent, and multipotent stem cells?

1. Totipotent: Can differentiate into any cell type, including placental cells (e.g., zygote).
2. Pluripotent: Can differentiate into any cell type in the body, but not placental cells (e.g., embryonic stem cells).
3. Multipotent: Can differentiate into a limited number of cell types within a specific lineage (e.g., adult stem cells like hematopoietic stem cells).

Therapeutic cloning involves creating an embryo to harvest stem cells for medical treatment.

embryonic

Differentiation

The process by which a less specialized cell becomes a more specialized cell type.

How do specialized cells in multicellular organisms arise from a single zygote?

Through cell division (mitosis) and differentiation, where cells selectively express certain genes to develop specific structures and functions.

Organelle

A specialized subunit within a cell that has a specific function.

The of a cell refers to all the material within a living cell, excluding the nucleus.

cytoplasm

What is the main difference in genetic material between prokaryotic and eukaryotic cells?

Prokaryotic cells have a circular chromosome in the nucleoid region, and often plasmids, while eukaryotic cells have multiple linear chromosomes enclosed within a nucleus.

Plasmid

Small, circular, extrachromosomal DNA molecules found in bacteria, capable of independent replication and often carrying genes for antibiotic resistance.