Cells Unit: Cell Theory, Organelles, Transport, and the Cell Cycle

Flashcards covering cell theory, eukaryotic and prokaryotic differences, cellular organelles, passive and active cell transport, homeostasis feedback loops, the cell cycle, mitosis, and cancer biology.

What are the three core principles of the Cell Theory?

1. All living things are made of cells.
2. Cells are the basic unit of life.
3. All cells come from other cells.

How do prokaryotic and eukaryotic cells differ in terms of their nucleus, organelles, cell division, and cell walls?

Prokaryotic cells have no nucleus, no membrane-bound organelles, divide by binary fission, are unicellular, and have cell walls made of peptidoglycan (e.g., bacteria). Eukaryotic cells have a nucleus, membrane-bound organelles, divide by mitosis, can be unicellular or multicellular, and only fungi (chitin) and plants (cellulose) possess cell walls.

What four cellular structures are present in ALL cells?

1. Genetic material ($\text{DNA}$ or $\text{RNA}$
2. Cytoplasm
3. Cell membrane
4. Ribosomes

What is the structural composition of the cell (plasma) membrane according to the Fluid Mosaic Model?

It is made of a phospholipid bilayer with polar hydrophilic (water-loving) heads and nonpolar hydrophobic (water-fearing) tails, embedded with proteins for transport and carbohydrates for structure.

What are the functions of the cytoskeleton and cytoplasm?

The cytoskeleton consists of threadlike protein fibers that give the cell shape, move organelles around, and provide structural support (especially in animal cells). The cytoplasm is a jelly-like fluid mainly composed of water that holds organelles in place.

What is the distinction between the nucleus and the nucleolus?

The nucleus protects genetic material ($\text{DNA}$) and is surrounded by a nuclear membrane with pores. The nucleolus is located inside the nucleus and makes $\text{rRNA}$, which comprises ribosomes.

What are the structural and functional differences between the Rough Endoplasmic Reticulum (ER) and Smooth Endoplasmic Reticulum (ER)?

Rough ER has ribosomes on its surface, hugs the nucleus, makes proteins, and packages them for secretion. Smooth ER lacks ribosomes, is attached to the Rough ER, and synthesizes lipids for the cell membrane.

How does the Golgi apparatus interact with proteins produced in the cell?

It consists of a folded membrane that receives transport vesicles containing proteins from the ER, then processes, sorts, and ships them to wherever they are needed.

What role do lysosomes play in animal cells?

They contain digestive enzymes that break down dead material, food, bacteria, and old cellular components, and can execute programmed cell death (apoptosis).

How do vacuoles differ between plant and animal cells?

Animal cells contain small and numerous vacuoles for storage, whereas plant cells contain one massive central vacuole that acts as a primary storage center for water, nutrients, and waste.

What is the function of centrioles (centrosomes) during animal cell division?

They are made of microtubules (two centrioles form a centrosome) that appear during cell division to pull duplicated chromosomes apart.

How do cilia and flagella differ in structure and function?

Cilia are shorter, more numerous, and move fluid across the cell surface. Flagella are longer, fewer in number ($1-3$), and propel the entire cell through extracellular fluid.

What are the structural components and primary function of the mitochondrion?

Composed of an inner membrane and a fluid matrix, it serves as the site of cellular respiration, breaking down food to produce energy stored in $ATP$.

What are the structural components and function of the chloroplast in plant cells?

Composed of stacks called grana and fluid called stroma, it is the site of photosynthesis, converting solar energy into chemical energy stored in sugar.

How does dynamic equilibrium differ from static equilibrium in the context of homeostasis?

Dynamic equilibrium is not completely static or fixed; instead, conditions fluctuate slightly while staying regulated within an acceptable physiological range.

What is the difference between a positive feedback loop and a negative feedback loop?

A positive feedback loop amplifies or intensifies the output of a system (e.g., human childbirth contractions or fruit ripening via ethylene release). A negative feedback loop counteracts the stimulus to return the system to a set point or stability (e.g., thermoregulation, osmoregulation, or blood sugar regulation).

Which types of molecules easily pass through the cell membrane, and which do not?

Molecules that easily pass are small, nonpolar, hydrophobic, neutral, and water. Molecules that cannot pass easily are large and/or polar molecules.

What fundamental difference distinguishes passive transport from active transport?

Passive transport requires no cellular energy ($ATP$) because molecules move down their concentration gradient from high to low concentration. Active transport requires $ATP$ energy to move molecules against their concentration gradient from low to high concentration.

Define the terms solute, solvent, and solution.

Solute is the substance that gets dissolved (e.g., lemonade powder). Solvent is the liquid that does the dissolving (e.g., water). Solution is the uniform mixture of two or more substances (e.g., lemonade).

What is simple diffusion and what substances typically cross via this method?

The passive spreading out of molecules across a membrane down their concentration gradient (from high to low concentration) until dynamic equilibrium is reached. Examples include small nonpolar molecules like $O_2$ and $CO_2$.

What is facilitated diffusion and what molecules rely on it?

A form of passive transport where a transport protein (acting as a channel or carrier) helps large molecules like glucose ($C_6H_{12}O_6$) or polar molecules/ions like calcium ($Ca^{2+}$) move down their concentration gradient.

How do hypertonic, hypotonic, and isotonic solutions affect cell volume during osmosis?

In a hypertonic solution, solute concentration is higher outside (lower water concentration), causing net water movement out of the cell and the cell shrivels. In a hypotonic solution, solute concentration is lower outside (higher water concentration), causing net water influx and the cell swells. In an isotonic solution, concentrations are equal, and the cell stays the same size.

How do molecular pumps operate during active transport?

They use $ATP$ energy to pump charged particles or ions (such as $K^+$, $Na^+$, $Ca^{2+}$, and $Cl^-$) across the membrane through a protein channel against their concentration gradient, allowing cells to concentrate nutrients or expel wastes rapidly.

What is the difference between endocytosis and exocytosis?

Endocytosis uses vesicles to engulf and bring large particles into the cell (e.g., white blood cells capturing bacteria). Exocytosis uses vesicles to secrete or export substances out of the cell (e.g., nerve cells releasing neurotransmitters).

What is the developmental timeline from fertilization to implantation?

Fertilization produces a single-cell zygote, which undergoes cleavage within $30\text{ hours}$, reaches the morula stage ($8\text{ cells}$) at $72\text{ hours}$, forms a blastocyst at $4\text{ days}$, and implants into the uterine wall at $6\text{ days}$.

How do embryonic stem cells differ from adult stem cells?

Embryonic stem cells are completely undifferentiated and can become any specialized cell type. Adult stem cells (found in adult bone marrow) are partially differentiated and can only develop into specific cell types.

List the levels of structural organization resulting from differentiation from simplest to most complex.

Cell $\rightarrow$ Tissue $\rightarrow$ Organ $\rightarrow$ Organ System $\rightarrow$ Organism.

What are the three sub-phases of interphase and what happens in each?

1. $G_1$ (Gap 1): Cell grows and synthesizes proteins.
2. $S$ (Synthesis): DNA replication occurs, doubling the chromosome content.
3. $G_2$ (Gap 2): Additional cell growth and protein synthesis occur.

In chromosome anatomy, what do the green, pink, and blue arrows identify in this diagram?

The green arrow points to the centromere (the pinched central region), while the pink and blue arrows point to the telomeres (the protective outer ends of the DNA molecule).

What are the four successive stages of mitosis and their defining cellular events?

1. Prophase: Chromosomes condense into visible sister chromatids (X's), the nuclear membrane disintegrates, and spindle fibers form.
2. Metaphase: Spindle fibers attach to centromeres and chromosomes line up along the middle of the cell.
3. Anaphase: Sister chromatids separate to opposite cell poles as individual chromosomes.
4. Telophase: Chromosomes decondense back into chromatin, nuclear membranes re-form at each pole, spindle fibers break down, and cytokinesis begins.

How does cytokinesis differ between animal cells and plant cells?

In animal cells, cytokinesis occurs through the formation of a cleavage furrow that pinches the cell into two equal daughter cells. In plant cells, a cell plate forms midway between the divided nuclei and gradually develops into a separating cell membrane.

Why must cells divide rather than simply growing larger to increase an organism's size?

Cells must stay small to maintain a high surface area to volume ratio, which optimizes metabolic energy efficiency and allows nutrients and wastes to move across the cell membrane quickly.

What are the typical division turnover rates for lining of intestines, skin cells, red blood cells, and liver cells?

• Internal lining of intestines: $5\text{ days}$
• Skin cells: every $2\text{ weeks}$
• Red blood cells: $4\text{ months}$
• Liver cells: $1\text{ year}$

What are the roles of cell cycle checkpoints and the $G_0$ resting state?

Checkpoints ($G_1$, $G_2$, and $M$) act as critical stop-and-go control points governed by regulatory proteins. In animal cells, the cycle is default 'off' unless stimulated. Without division signals, cells enter the non-dividing $G_0$ resting state.

What is apoptosis and what is an example of its normal role in human development?

Apoptosis is programmed cell death triggered by internal or external signals that activate self-destructive enzymes. An example is the removal of webbing between human fingers and toes during embryonic development.

What distinguishes benign tumors from malignant tumors, and what does it mean to metastasize?

Benign tumors consist of abnormal cells that remain clustered together, are usually harmless, and can be easily removed. Malignant tumors consist of cancer cells that break away, enter the bloodstream or lymphatic vessels, and invade distant tissues. Metastasize refers to this spread of disease from one organ to another.

What are carcinogens and what are notable examples of factors that cause cancer?

Carcinogens are chemicals or agents that induce cancer by mutating DNA. Examples include tobacco smoke and asbestos, alongside biological factors (inherited mutations, age), lifestyle choices (poor diet, UV radiation), and viruses (e.g., HPV causing cervical cancer).