Cell structure basics
56 flashcards covering Cell structure basics for the ACT Science section.
Cell structure basics involve understanding the fundamental building blocks of life: cells. Every living organism is made up of one or more cells, which are tiny units containing specific parts that perform essential functions. For example, the cell membrane acts as a protective barrier, the nucleus stores genetic information, and organelles like mitochondria produce energy. This topic is a cornerstone of biology, helping you grasp how organisms function at a microscopic level, which is crucial for broader scientific concepts.
On the ACT Science section, cell structure often appears in questions that test your ability to interpret diagrams, graphs, or data tables about cell components and their roles. Common question types include identifying functions of organelles, comparing plant and animal cells, or analyzing experimental results on cell processes. Watch out for traps like confusing similar structures—such as mistaking the endoplasmic reticulum for the Golgi apparatus—or overlooking key details in passages. Focus on memorizing main cell parts and their interactions to handle these efficiently.
A helpful tip: Practice sketching a basic cell to visualize and remember the key structures.
Terms (56)
- 01
Cell
The basic structural and functional unit of all living organisms, consisting of a membrane-bound structure that contains organelles and genetic material.
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Cell theory
A fundamental principle stating that all living things are made of cells, cells are the smallest units of life, and all cells come from pre-existing cells.
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Prokaryotic cell
A simple type of cell without a nucleus or membrane-bound organelles, found in bacteria and archaea, with genetic material in the cytoplasm.
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Eukaryotic cell
A complex type of cell with a nucleus and membrane-bound organelles, found in plants, animals, fungi, and protists, allowing for specialized functions.
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Cell membrane
A phospholipid bilayer that surrounds the cell, regulating what enters and leaves by controlling permeability and containing proteins for transport and signaling.
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Phospholipid bilayer
The main structure of the cell membrane, consisting of two layers of phospholipid molecules with hydrophobic tails inside and hydrophilic heads facing water.
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Nucleus
The organelle in eukaryotic cells that houses the cell's DNA and controls cellular activities by regulating gene expression and cell division.
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Chromatin
The complex of DNA and proteins that forms chromosomes in the nucleus, condensing into visible chromosomes during cell division.
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Nucleolus
A dense region within the nucleus where ribosomal RNA is synthesized and ribosomes are assembled for protein production.
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Mitochondrion
An organelle in eukaryotic cells that produces energy in the form of ATP through cellular respiration, often called the powerhouse of the cell.
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Chloroplast
An organelle in plant cells and some protists that conducts photosynthesis, converting sunlight, carbon dioxide, and water into glucose and oxygen.
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Ribosome
A cellular structure composed of RNA and proteins that assembles amino acids into proteins by translating messenger RNA instructions.
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Endoplasmic reticulum
A network of membranes in eukaryotic cells involved in protein and lipid synthesis; rough ER has ribosomes, while smooth ER does not.
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Rough endoplasmic reticulum
The part of the ER studded with ribosomes, where proteins destined for secretion or membranes are synthesized and folded.
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Smooth endoplasmic reticulum
The part of the ER without ribosomes, involved in lipid synthesis, detoxification, and calcium storage in cells.
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Golgi apparatus
An organelle that modifies, sorts, and packages proteins and lipids from the ER into vesicles for transport to other parts of the cell or outside.
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Lysosome
A membrane-bound organelle containing enzymes that break down waste materials, cellular debris, and engulfed particles in animal cells.
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Vacuole
A large, membrane-bound sac in plant and fungal cells that stores water, nutrients, and waste, and helps maintain turgor pressure.
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Central vacuole
The large vacuole in mature plant cells that occupies most of the cell volume, aiding in storage, waste disposal, and structural support.
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Cytoplasm
The jelly-like substance inside the cell membrane but outside the nucleus, where organelles are suspended and metabolic reactions occur.
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Cytoskeleton
A network of protein fibers in the cytoplasm that provides structural support, enables cell movement, and helps transport organelles.
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Microtubules
Hollow tubes made of tubulin proteins that are part of the cytoskeleton, aiding in cell shape, division, and movement of organelles.
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Microfilaments
Thin filaments made of actin proteins in the cytoskeleton that enable cell movement, contraction, and changes in cell shape.
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Cell wall
A rigid layer outside the cell membrane in plant cells, bacteria, and fungi, providing structural support and protection.
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Plant cell
A eukaryotic cell with a cell wall, chloroplasts, and a large central vacuole, specialized for photosynthesis and structural rigidity.
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Animal cell
A eukaryotic cell without a cell wall or chloroplasts, featuring a flexible membrane and lysosomes for waste breakdown.
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Organelle
A specialized structure within a cell that performs distinct functions, such as energy production or protein synthesis.
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Selective permeability
The property of the cell membrane that allows only certain substances to pass through, controlling the internal environment.
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Diffusion
The passive movement of molecules from an area of higher concentration to lower concentration until equilibrium is reached.
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Osmosis
The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to higher.
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Hypotonic solution
A solution with a lower solute concentration than inside the cell, causing water to enter and potentially swell the cell.
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Isotonic solution
A solution with the same solute concentration as inside the cell, resulting in no net water movement.
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Hypertonic solution
A solution with a higher solute concentration than inside the cell, causing water to leave and the cell to shrink.
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Active transport
The energy-requiring process that moves substances across the cell membrane against their concentration gradient using proteins.
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Endocytosis
The process by which a cell takes in substances by engulfing them with its membrane, forming a vesicle.
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Exocytosis
The process by which a cell expels substances by fusing vesicles with the cell membrane and releasing contents outside.
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Surface area to volume ratio
A key factor in cell size, calculated as the cell's surface area divided by its volume, which limits how large cells can grow for efficient exchange.
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Common trap: Prokaryotes vs. eukaryotes
Students often confuse prokaryotes as having no DNA; actually, they have DNA in the cytoplasm, while eukaryotes have it in a nucleus.
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Function of mitochondria
To generate ATP through aerobic respiration, using oxygen to break down glucose and provide energy for cellular activities.
- 40
Function of chloroplasts
To capture sunlight for photosynthesis, producing glucose from carbon dioxide and water, which is then used for energy.
- 41
Plasma membrane proteins
Proteins embedded in or attached to the membrane that facilitate transport, signaling, and cell recognition.
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Cell division in prokaryotes
Occurs through binary fission, where the cell replicates its DNA and splits into two identical daughter cells.
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Cell division in eukaryotes
Involves mitosis for somatic cells, where the nucleus divides after DNA replication, followed by cytokinesis.
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Flagella
Whip-like structures on some cells, made of microtubules, that enable movement by propelling the cell through its environment.
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Cilia
Short, hair-like projections on cell surfaces, composed of microtubules, that move to sweep substances or propel the cell.
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Nuclear envelope
A double membrane surrounding the nucleus, with pores that allow selective passage of molecules between the nucleus and cytoplasm.
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Peroxisome
An organelle that breaks down fatty acids and detoxifies harmful substances using enzymes that produce hydrogen peroxide.
- 48
Centriole
A structure in animal cells that helps organize microtubules during cell division, forming the spindle apparatus.
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Strategy for identifying cell types
Examine for presence of a nucleus and organelles; prokaryotes lack these, while eukaryotes have them, and plant cells have chloroplasts.
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Example of osmosis in cells
When a plant cell is placed in hypotonic water, it swells as water enters, demonstrating how osmosis maintains turgor pressure.
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Common trap: Chloroplast location
Chloroplasts are only in plant cells and some protists, not animal cells, so don't assume all cells perform photosynthesis.
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Membrane fluidity
The ability of the cell membrane to change shape, influenced by temperature and cholesterol, allowing flexibility for transport and signaling.
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Integral membrane proteins
Proteins that span the phospholipid bilayer, often serving as channels or pumps for substance transport across the membrane.
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Peripheral membrane proteins
Proteins attached to the surface of the membrane, involved in support, enzymatic activity, or signaling without penetrating the bilayer.
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Worked example: Cell membrane transport
In a cell, glucose enters via facilitated diffusion through channel proteins when concentration is higher outside, illustrating selective permeability.
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Bacterial cell structure
Includes a cell wall, plasma membrane, cytoplasm, ribosomes, and a single circular DNA molecule, but no nucleus or mitochondria.