Module 1: Cells as the basis of life

HSC PRELIMINARY BIOLOGY MODULE ONE

Light Microscope

A microscope that uses visible light and lenses to magnify specimens. It provides lower resolution images, allowing observation in color, and can display specimens in 2D or 3D.

Electron Microscope

A microscope that uses electron beams to magnify specimens, offering high-resolution imaging. It produces black and white images and can display specimens in 2D (TEM) or 3D (SEM).

Prokaryotic Cells

Cells that lack a nucleus and other membrane-bound organelles. They are typically small (1–10 µm) and include organisms like Bacteria and Archaea.

Eukaryotic Cells

Cells that contain a nucleus and other membrane-bound organelles. They are generally larger (10–100 µm) and include organisms like Plants, Animals, Fungi, and Protists.

Nucleus

A membrane-bound organelle within eukaryotic cells that contains DNA. It controls cell activities and stores genetic information.

Mitochondria

Double-membrane organelles found in eukaryotic cells, characterized by a folded inner membrane. They are the site of aerobic respiration and ATP (energy) production.

Ribosomes

Small particles, either free or attached to the endoplasmic reticulum (ER), that are essential for protein synthesis within cells.

Endoplasmic Reticulum (ER)

A network of membranes within eukaryotic cells that is involved in protein and lipid synthesis. It includes the Rough ER (with ribosomes) for protein transport and the Smooth ER (without ribosomes) for lipid synthesis.

Golgi Apparatus

An organelle in eukaryotic cells composed of stacked membranes that processes, packages, and modifies proteins and lipids for transport to other parts of the cell or for secretion.

Lysosomes

Vesicles within cells that contain enzymes for breaking down waste materials and old cell parts, acting as the cell's digestive system.

Chloroplasts

Double-membrane organelles found in plant cells and some protists, containing chlorophyll. They facilitate photosynthesis, converting light energy into chemical energy.

Vacuole

A fluid-filled sac within cells used for the storage of various substances, such as water, nutrients, and waste products. They are notably larger in plant cells.

Cell Membrane

A biological membrane consisting of a phospholipid bilayer, which controls the entry and exit of substances in a cell, maintaining cell integrity.

Cell Wall

A rigid outer layer found in plant cells, fungi, and bacteria, providing structural support and protection to the cell. In plants, it is primarily made of cellulose.

Diffusion

A type of passive transport where substances move from an area of high concentration to an area of low concentration without requiring energy. Example: oxygen moving into cells.

Osmosis

A type of passive transport involving the movement of water molecules across a selectively permeable membrane from an area of high water concentration to an area of low concentration. Example: water entering plant root cells.

Facilitated Diffusion

A type of passive transport where substances move from an area of high concentration to an area of low concentration with the help of membrane proteins (channels or carriers). Example: glucose transport into cells.

Active Transport

A type of transport that requires energy (ATP) to move substances across a cell membrane against their concentration gradient (from low to high concentration). Example: sodium-potassium pump.

Endocytosis

A process where cells engulf substances by surrounding them with the cell membrane, forming a vesicle and bringing the substance into the cell. Requires energy. Example: white blood cells engulfing bacteria.

Exocytosis

A process where cells expel substances by fusing vesicles containing the substances with the cell membrane, releasing the contents outside the cell. Requires energy. Example: neurotransmitter release.

Hypotonic Solution

A solution that causes water to move into the cell because it has a lower solute concentration than the cell. This can cause animal cells to swell or burst and plant cells to become turgid (firm).

Hypertonic Solution

A solution that causes water to move out of the cell because it has a higher solute concentration than the cell. This can cause animal cells to shrink (crenation) and plant cells to undergo plasmolysis (membrane pulls away from the cell wall).

Isotonic Solution

A solution where there is no net water movement because the solute concentration is the same inside and outside the cell. This results in normal animal cells and flaccid (limp) plant cells.

Cell Theory

A fundamental principle in biology stating that all living things are made up of cells, all cells come from pre-existing cells, and the cell is the basic unit of life.

Selective Permeability

The property of a cell membrane that allows only certain substances to pass through while restricting others, based on factors like size, charge, and solubility.

Concentration Gradient

The difference in solute concentration between two adjacent areas or compartments, which drives diffusion and osmosis.

Hydrophilic Molecules

Molecules that are soluble in water (water-loving) but have difficulty passing through cell membranes due to their polarity.

Hydrophobic Molecules

Molecules that are not soluble in water (water-fearing) and can easily pass through the lipid bilayer of cell membranes.

Heterotrophic Organism

An organism that obtains nutrition by consuming other organisms or organic matter, unable to produce its own food.

Autotrophic Organism

An organism that produces its own food using energy from sunlight or chemical sources, typically through photosynthesis.

Inorganic Compounds

Chemical compounds that generally do not contain both carbon and hydrogen atoms; they are often simple and associated with non-living matter.

Organic Compounds

Chemical compounds that contain both carbon and hydrogen atoms; they are typically complex and associated with living organisms.

Carbohydrate

Organic molecules composed of carbon, hydrogen, and oxygen atoms, serving as a primary source of energy for cells. Examples include sugars, starches, and cellulose.

Lipid

Organic molecules including fats, oils, and waxes, composed mainly of carbon and hydrogen atoms. They store energy, form cell membranes, and act as insulation.

Protein

Large, complex organic molecules composed of amino acids. They perform numerous cellular functions, including catalyzing reactions, transporting molecules, and providing structure.

Nucleic Acid

Large organic molecules, such as DNA and RNA, that store and transmit genetic information within cells.

Cytosis

The process of transporting large quantities of molecules into or out of cells, including endocytosis (into the cell) and exocytosis (out of the cell).

Cell Membrane Function

The role of the cell membrane in controlling the movement of substances between the cell's internal and external environments, maintaining cell homeostasis.

Additional Cell Membrane Functions

Additional roles of the cell membrane, including cell recognition (identifying other cells) and communication (sending and receiving signals).

Fluid Mosaic Model

A model describing the cell membrane as a 'lipid sea' with diverse proteins floating within it, supported by evidence from membrane behavior, chemical analysis, and electron microscopy.

Phospholipid Bilayer

An arrangement of phospholipid molecules in two layers, forming the basic structure of cell membranes. Hydrophilic (water-attracting) heads face outwards, and hydrophobic (water-repelling) tails face inwards.

Proteins in Cell Membrane

Proteins embedded within the phospholipid bilayer of cell membranes, some spanning both layers as channels or carriers. Many are glycoproteins with carbohydrates attached for cell recognition.

Other Components of Cell Membrane

Other molecules found in the cell membrane, including carbohydrates (glycolipids and glycoproteins) that act as cell markers, microtubules for cytoskeleton anchorage, and cholesterol for structure regulation.

Evidence for the Fluid Mosaic Model

Evidence supporting the fluid mosaic model, including the easy passage of lipid-soluble substances, the ability of membranes to reseal when punctured, and electron microscopy showing a lipid center with dispersing proteins.

Permeability Types

Classification of cell membranes based on permeability: impermeable (nothing passes), permeable (all passes), and selectively permeable (only certain substances pass).

Factors Affecting Membrane Transport

Factors influencing the movement of molecules across cell membranes, including the molecule’s size, charge (polarity), and lipid solubility.

Movement Across Cell Membrane

Mechanisms by which substances move across the cell membrane: lipid-soluble molecules pass easily, water-soluble molecules use carrier proteins, and water moves by osmosis through hydrophilic pores.