AP Bio Unit 2 Part 1 Gaps

What are the 3 parts of cell theory?

All living things are made of cells. Cells are the basic unit of life. Cells only come from pre-existing cells.

What does "cells are the basic unit of life" actually mean?

The cell is the smallest thing that still counts as alive. Parts pulled out of a cell, like a ribosome, can't carry out life on their own.

As a cell grows, what happens to its SA:V ratio, and why is that a problem?

SA:V shrinks because volume grows faster than surface area. There's too little membrane to supply all the cytoplasm by diffusion, so the inside starves.

Folded membranes show up all over the cell (cristae, thylakoids, microvilli). What's the shared reason?

Folding adds surface area without adding volume, so more membrane-based work (like making ATP or absorbing nutrients) fits in the same space.

What's wrong with this statement: "Prokaryotes have no membranes"?

Every prokaryote has a plasma membrane, which is what makes it a cell. What they lack is membrane-BOUND ORGANELLES like a nucleus, ER, Golgi, or mitochondria.

Do prokaryotes have mitochondria? Use endosymbiosis to explain.

No. Mitochondria are descended from prokaryotes that early eukaryotes engulfed, so a prokaryote can't contain one.

Prokaryotes have no membrane-bound organelles. Which protein-making structure do they still have, and why is that allowed?

Ribosomes. Ribosomes have no membrane, so they don't count as membrane-bound. (Prokaryotic ribosomes are smaller than eukaryotic ones.)

Where is a prokaryote's DNA, and why isn't that called a nucleus?

In the nucleoid region. It's just an area of cytoplasm with no membrane around it, while a nucleus is enclosed by a double membrane.

Your teacher calls prokaryotes "not specialized" and eukaryotes "specialized." Specialized in what way?

Eukaryotes have membrane-bound organelles, separate compartments where specific jobs happen under their own conditions (like the acidic inside of a lysosome). Prokaryotes do everything in one open space.

Bacteria vs archaea: what's the same and what's different?

Both are prokaryotes with no nucleus. Bacterial walls contain peptidoglycan, archaea walls don't. Archaea also have chemically different membranes and often live in extreme environments.

What's wrong with calling animal cells "chemoautotrophic"?

Auto means self-feeding, and animals can't make their own food. Animal cells are CHEMOHETEROTROPHIC: they get energy and carbon by eating molecules other organisms made.

Break "chemoheterotrophic" into its word parts.

Chemo = energy from chemicals, hetero = other, troph = feeding. "Gets energy by feeding on chemicals made by others."

Break "photoautotrophic" into its word parts. Which cell type is it?

Photo = light, auto = self, troph = feeding. "Feeds itself using light." Plant cells, using chloroplasts.

Chemoautotrophs are real organisms. What are they, and why can't an animal be one?

Bacteria or archaea that make their own food using energy from inorganic chemicals (like at deep-sea vents). Animals can't make their own food at all, so they can't be autotrophs of any kind.

Name 3 structures plant cells have that animal cells don't.

A cell wall (cellulose), chloroplasts, and a large central vacuole.

Secretory vesicles release proteins by exocytosis. Do they fuse with the cell wall or the plasma membrane?

The plasma membrane. The cell wall is non-living and structural only.

Why can't "vesicles ship proteins to the cell wall" be right? Think about animal cells.

Animal cells have no cell wall. If vesicles went to the wall, animal cells could never secrete insulin, antibodies, or digestive enzymes.

In a plant cell, which is further outside: the cell wall or the plasma membrane?

The cell wall. It sits outside the plasma membrane. Walled cells have BOTH, and the membrane still controls what enters and leaves.

Living, selectively permeable, found in every cell. Cell wall or plasma membrane?

Plasma membrane.

Non-living, freely permeable, structural only, found only in plants, fungi, and bacteria. Cell wall or plasma membrane?

Cell wall.

On an animal cell diagram, what should the outer boundary be labeled?

Plasma membrane (a phospholipid bilayer). Not cell wall. Animal cells don't have one.

What are the holes in the nuclear envelope called, and what passes through them in each direction?

Nuclear pores. OUT: mRNA and ribosome subunits. IN: proteins the nucleus needs.

Why does the nucleus need pores at all?

mRNA and proteins are too large and polar to cross a phospholipid bilayer, so they need protein-lined openings.

Describe the nuclear envelope's structure and what it connects to.

A double membrane (two bilayers) perforated with nuclear pores. Its outer membrane continues directly into the ER.

What exactly does the nucleolus make, and does it have a membrane?

rRNA, which it assembles into ribosome subunits. No membrane. It's just a dense region inside the nucleus.

Eukaryotic DNA is ______. Bacterial DNA is ______.

Linear (inside the nucleus). Circular (in the nucleoid region).

What decides whether a ribosome ends up free or attached to the rough ER?

The protein it's making. If the start of the protein carries a "ship me out" signal, the ribosome gets pulled onto the ER. It's the same kind of ribosome either way.

Free vs bound ribosomes: where does each one's protein end up?

Free: stays inside the cell (cytoplasm and organelles). Bound: goes to the plasma membrane, to lysosomes, or out of the cell.

Give 3 examples of proteins made by ribosomes on the rough ER.

Insulin, antibodies, and digestive enzymes. Also membrane proteins and lysosome enzymes.

After ribosomes build a protein into the rough ER, what does the ER do to it?

Folds it into its 3D shape, adds sugar tags, and destroys misfolded proteins before sending good ones to the Golgi.

Which cells have the most rough ER, and why?

Cells that export lots of protein, like pancreas cells (insulin, digestive enzymes) and white blood cells (antibodies).

Name 4 jobs of the smooth ER.

Makes lipids (phospholipids and steroid hormones), detoxifies drugs and alcohol, breaks down glycogen into glucose, and stores calcium in muscle cells.

Where would you find cells packed with smooth ER, and which job explains each?

Liver (detox and glycogen breakdown), testes and ovaries (steroid hormones like testosterone and estrogen), muscle (calcium storage).

What does "flattened extension of the nuclear membrane" mean for the ER?

The outer layer of the nuclear envelope continues outward into the ER. They're one continuous membrane.

Which face of the Golgi receives and which ships, and which way does each face point?

Cis receives and faces the ER. Trans ships and faces the plasma membrane.

Which organelle does the cis face of the Golgi face, and where were the incoming proteins made?

The ER in general (not specifically the smooth ER). The incoming proteins were made by ribosomes on the rough ER.

Where does the trans face of the Golgi send its vesicles? Name 2 destinations.

To the plasma membrane (to be secreted by exocytosis or become membrane proteins) and to become lysosomes. Never the cell wall.

What two kinds of tags does the Golgi add to proteins, and what are they for?

Sugar tags and phosphate tags. They work like shipping addresses so each protein goes to the right place.

Where do lysosomes come from?

They bud off the trans face of the Golgi, which packs them with hydrolytic enzymes.

What does "hydrolytic" mean, and how do hydrolytic enzymes break molecules?

Hydro = water, lytic = splitting. They split big molecules by inserting water into the bonds (hydrolysis).

Why doesn't a leaking lysosome digest the whole cell?

Its enzymes only work at about pH 5, the lysosome's acidic inside. The cytoplasm is about pH 7.2, so leaked enzymes mostly shut off.

When a lysosome recycles a worn-out organelle, what is the organelle turned into, and where does it go?

Monomers (amino acids, sugars, fatty acids, nucleotides). They're released into the cytoplasm to build new parts.

Give 2 examples of apoptosis during normal development.

The webbing between fingers dissolving in the womb, and a tadpole losing its tail.

Why is failed apoptosis linked to cancer?

Cells with damaged DNA are supposed to self-destruct. If apoptosis fails, they keep dividing instead.

What's wrong with this statement: "In Tay-Sachs, the lysosomes fail"?

The lysosome still works. Only ONE enzyme is missing, so the one molecule it digests builds up and swells the lysosome.

Tay-Sachs: what builds up, in which cells, and why is it fatal?

A lipid builds up in brain nerve cells. Nerve cells aren't replaced, so function is permanently lost as they die.

What's wrong with calling a peroxisome a "specialized lysosome"?

They only look alike. Peroxisomes don't come from the Golgi, they make more of themselves by splitting, and their enzymes are oxidative instead of hydrolytic.

Lysosome vs peroxisome: how is each one made?

Lysosome: buds off the Golgi. Peroxisome: imports proteins straight from the cytoplasm, grows, and splits in half.

Lysosome enzymes are ______. Peroxisome enzymes are ______.

Hydrolytic (break bonds using water). Oxidative (break bonds by removing hydrogen and handing it to oxygen).

Where does the H₂O₂ inside a peroxisome come from?

The peroxisome makes it. It's a byproduct of its own oxidation reactions (breaking down fatty acids and toxins).

What enzyme destroys H₂O₂, and what's the reaction?

Catalase. 2 H₂O₂ → 2 H₂O + O₂

Why does hydrogen peroxide bubble when you pour it on a cut?

Catalase from your damaged cells splits it into water and oxygen gas. The bubbles are O₂.

What does the peroxisome do to fatty acids, and which organelle finishes the job?

It chops long fatty acids into small pieces (beta-oxidation). The mitochondria burn those pieces for ATP.

Which two organelles detoxify the cell, and which organ has lots of both?

Smooth ER and peroxisomes. The liver.

What's the correct name for the huge vacuole in plant cells, and what 3 things does it hold?

The central vacuole. It holds water, pigments, and starch.

Turgor pressure needs TWO structures. What are they and what does each do?

The central vacuole pushes outward with water pressure, and the cell wall pushes back. Together they keep non-woody plants upright.

What happens to a food vacuole after it forms?

It fuses with a lysosome, and the lysosome's hydrolytic enzymes digest the food.

Which organisms are best known for food vacuoles?

Protists that eat by engulfing food (phagocytosis), like amoebas and paramecia.

Why is "vacuoles are permanent, vesicles aren't" a bad rule? What's better?

Food vacuoles get digested and disappear, so vacuoles aren't always permanent. Size is the safer difference: vacuoles are bigger.

Mitochondria: which part makes ATP and which part releases CO₂?

The cristae (folded inner membrane) make ATP. The matrix (fluid inside) releases CO₂ during the Krebs cycle.

The CO₂ you breathe out: where in your cells was it made?

In the matrix of your mitochondria, during the Krebs cycle.

What does "catabolic" mean, and which organelle is catabolic?

Cata = down. Catabolic reactions break big molecules into small ones and RELEASE energy. Mitochondria (breaking glucose down for ATP).

Why do you inherit mitochondria only from your mother?

The egg supplies basically all of the embryo's mitochondria. Sperm contribute essentially none.

What's wrong with this statement: "Chloroplasts have the same function as mitochondria"?

They do the opposite. Chloroplasts BUILD sugar from CO₂ (anabolic). Mitochondria BREAK sugar down (catabolic).

What's wrong with this statement: "Chloroplasts convert carbon into ATP"?

The final product is sugar, not ATP. Thylakoids make ATP from light, then the stroma SPENDS that ATP building sugar from CO₂.

Thylakoid vs stroma: which makes ATP and which makes sugar?

Thylakoids (stacked membrane discs) use light to make ATP. The stroma (fluid around them) builds sugar from CO₂ in the Calvin cycle.

If chloroplasts make ATP, why do plant cells still need mitochondria?

The chloroplast's ATP gets used up inside the chloroplast to build sugar. To power the rest of the cell, the plant breaks that sugar down in its mitochondria.

What does "anabolic" mean, and which organelle is anabolic?

Ana = up. Anabolic reactions build big molecules from small ones and USE energy. Chloroplasts (building glucose from CO₂).

How are the photosynthesis and cellular respiration equations related?

They're the same reaction running in opposite directions. Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP.

Complete the analogy. Matrix is to mitochondria as ______ is to chloroplast. Cristae are to mitochondria as ______ are to chloroplast.

Stroma (the fluid cavity). Thylakoids (the folded membrane that makes ATP).

Where exactly is chlorophyll, and what does it do?

In the thylakoid membranes. It absorbs light energy.

Fill in the blank: An early eukaryote engulfed a prokaryote, and instead of ______ it, the host kept it alive.

Digesting. The engulfed prokaryote kept making ATP, eventually lost the ability to live alone, and became the mitochondrion.

Which was engulfed first, the ancestor of mitochondria or of chloroplasts? How do we know?

Mitochondria. Almost all eukaryotes have mitochondria but only plants and algae have chloroplasts, so the chloroplast ancestor was engulfed later by a cell that already had mitochondria.

List 5 pieces of evidence that mitochondria and chloroplasts were once free-living bacteria.

Circular DNA, their own bacterial-sized ribosomes, a double membrane, they reproduce by splitting in two like bacteria, and they're bacteria-sized.

Some antibiotics block bacterial ribosomes. Which human organelle can they sometimes interfere with too, and why?

Mitochondria. They have bacterial-type ribosomes (leftover from endosymbiosis), so the drug can jam their protein-making too.

What's wrong with this statement: "Microtubules are made of small, hollow spheres"?

The subunits aren't hollow. The TUBE is. Tubulin pairs stack into strands, and 13 strands wrap into a hollow cylinder.

Name 3 jobs of microtubules.

Pull chromosomes apart during cell division (the spindle), build cilia and flagella, and act as tracks that vesicles travel along.

What is the centrosome, and what does it contain in animal cells?

The area near the nucleus where microtubules are organized. It contains a pair of centrioles.

What are microfilaments made of, and what shape are they?

Actin. Two actin chains twisted around each other like a two-strand rope.

Microtubules mainly resist ______. Microfilaments mainly resist ______.

Compression (pushing). Tension (pulling).

How do microfilaments make a muscle contract?

Myosin grabs actin filaments and pulls them past each other hand-over-hand, which shortens the muscle cell.

During animal cell division, which fiber separates the chromosomes and which pinches the cell in two?

Microtubules separate the chromosomes. A ring of actin microfilaments tightens to form the cleavage furrow.

How does an amoeba or white blood cell crawl?

Actin microfilaments push the membrane out into a pseudopod ("false foot"), and the cell flows into it.

Where are microfilaments densest, and what do they do there?

Right under the plasma membrane, forming a mesh that shapes and strengthens the cell surface.

What's wrong with this statement: "Intermediate filaments are permanent because they're twisted"?

Microfilaments are twisted too, so twisting can't be the reason. Just know the facts: intermediate filaments are built from fibrous proteins and are permanent.

What's wrong with this statement: "Intermediate filaments make keratin"?

They're MADE OF keratin (in some cells). Keratin is the protein they're built from.

Which cytoskeleton fiber is permanent, and what jobs does that make it good for?

Intermediate filaments. They're load-bearing: they anchor the nucleus and connect cells together so tissues resist tearing.

What do your hair, nails, and outer skin have in common at the cell level?

They're dead cells left with mostly their keratin intermediate filaments.

What makes cilia and flagella bend?

The motor protein dynein grabs neighboring microtubule pairs and makes them slide against each other.

Why are cilia and flagella called "cytoplasmic skeleton extensions"?

They're microtubules from the cytoskeleton pushed out past the cell body, with the plasma membrane stretched over them.

How are bacterial flagella different from eukaryotic flagella?

They have no microtubules and they spin like a propeller instead of whipping. Same name, unrelated structure.

What's wrong with this statement: "Unsaturated tails are more fluid because they have no rigid double bonds"?

The reason is backwards. Unsaturated tails HAVE double bonds. The double bonds cause kinks, and kinked tails can't pack tightly, so the membrane stays fluid.

Saturated tail: double bonds? Shape? Effect on the membrane?

No double bonds. Straight. Packs tightly, making the membrane stiffer.

Unsaturated tail: double bonds? Shape? Effect on the membrane?

At least one double bond. Kinked. Can't pack tightly, making the membrane more fluid.

What does "saturated" literally mean in a fatty acid?

Every carbon holds the most hydrogens possible (saturated with hydrogen). That's only possible with no double bonds.

Butter is solid at room temperature and olive oil is liquid. Which has more unsaturated fat, and why does that make it liquid?

Olive oil. Its kinked unsaturated tails can't pack together, so it stays liquid. Butter's straight saturated tails pack into a solid.

Why is the membrane called a "fluid mosaic"?

Fluid: phospholipids and proteins drift sideways constantly. Mosaic: it's a patchwork of different molecules (lipids, proteins, cholesterol, sugars).

Which part of the membrane actually blocks charged and polar molecules: the heads or the tails?

The tails. The nonpolar core in the middle is the barrier, because charged and polar molecules can't dissolve through it.

Why do O₂ and CO₂ cross the membrane freely?

They're small and nonpolar, so they dissolve right through the nonpolar core ("like dissolves like").

Ions like Na⁺ are tiny, yet they can't cross the bilayer. What does that prove?

Charge matters more than size. The nonpolar core repels anything charged, however small.