Cellular Energetics, Respiration, Photosynthesis, and Membrane Transport

Comprehensive fill-in-the-blank practice flashcards covering thermodynamics and metabolism, cellular respiration pathways, photosynthesis light reactions and the Calvin cycle, and membrane transport dynamics.

Catabolic pathways release energy by breaking down complex molecules into simpler compounds, whereas __________ pathways consume energy to build complicated molecules from simpler ones.

anabolic

The First Law of Thermodynamics states that energy can be transferred and transformed, but it cannot be __________ or destroyed.

created

According to the Second Law of Thermodynamics, every energy transfer or transformation increases the __________ of the universe.

entropy

Chemical reactions that have a negative change in free energy ($\Delta G < 0$) and occur without an external input of energy are classified as __________.

spontaneous (exergonic)

The cellular strategy of using an exergonic process to drive an endergonic process is referred to as __________.

energy coupling

In the chemical structure of adenosine triphosphate (ATP), the nitrogenous base attached to the ribose sugar is __________.

adenine

Enzymes speed up metabolic reactions by lowering the __________ barrier without changing the overall $\Delta G$ of the reaction.

activation energy ($E_A$)

Enzyme inhibitors that bind directly to the active site and mimic the substrate are called competitive inhibitors, whereas inhibitors that bind to another site on the enzyme to change its shape are called __________ inhibitors.

noncompetitive

In the feedback inhibition of isoleucine biosynthesis, accumulation of isoleucine slows down the pathway by binding to an allosteric site on the first enzyme, __________.

threonine deaminase

In a redox reaction, the loss of electrons from a substance is called oxidation, while the addition of electrons to another substance is called __________.

reduction

In the overall equation for cellular respiration ($C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}$), glucose becomes oxidized and oxygen becomes __________.

reduced

In cellular respiration, high-energy electrons extracted from food are first transferred to the oxidized coenzyme electron carrier __________.

$$NAD^+$$

While substrate-level phosphorylation produces a small amount of ATP during glycolysis and the citric acid cycle, almost $90\%$ of ATP is generated by __________.

oxidative phosphorylation

For each molecule of glucose processed during glycolysis, there is a net production of 2 pyruvate, 2 NADH, and __________ molecules of ATP.

$$2$$

Prior to entering the citric acid cycle, pyruvate is transported into the mitochondrion and converted to __________, releasing one molecule of $CO_2$ and producing one NADH.

acetyl CoA

In the initial step of the citric acid cycle, the two-carbon acetyl group of acetyl CoA combines with the four-carbon molecule __________ to form the six-carbon compound citrate.

oxaloacetate

In the ATP synthase molecular machine, protons pass into the matrix through the rotor and stator, rotating the internal rod to activate ATP generation at the __________.

catalytic knob

In the absence of oxygen, yeast cells undergo alcohol fermentation by converting pyruvate first into acetaldehyde and then into __________ to regenerate $NAD^+$ for glycolysis.

ethanol

The key allosteric enzyme that synchronizes the rate of glycolysis with the cell's energetic needs is __________, which is inhibited by ATP and citrate and stimulated by AMP.

phosphofructokinase

Organisms that generate their own organic molecules from inorganic materials using the energy of sunlight are known as __________.

photoautotrophs

Carbon dioxide enters leaves and oxygen exits through microscopic pores called __________.

stomata

Photosynthesis is partitioned into two stages: the light reactions occurring in the thylakoid membranes, and the Calvin cycle occurring in the __________.

stroma

The light-absorbing porphyrin ring head of a chlorophyll molecule is centered around an atom of __________.

magnesium ($Mg$)

Photosystem II has a reaction-center chlorophyll a pair known as P680, whereas the reaction-center chlorophyll a of Photosystem I is designated as __________.

P700

During linear electron flow in the light reactions, an enzyme associated with Photosystem II extracts electrons by splitting molecules of __________, releasing oxygen gas.

water ($H_2O$)

For the net synthesis of one molecule of the three-carbon sugar __________, the Calvin cycle must turn three times, fixing three molecules of $CO_2$.

glyceraldehyde-3-phosphate (G3P)

On hot, dry days, stomatal closure favors a wasteful process known as __________, in which rubisco binds $O_2$ instead of $CO_2$, consuming ATP and releasing $CO_2$ without producing sugar.

photorespiration

C4 plants avoid photorespiration by using the enzyme PEP carboxylase to fix carbon in mesophyll cells before exporting four-carbon malate into __________ for the Calvin cycle.

bundle-sheath cells

Desert-adapted CAM plants minimize daytime water loss by opening their stomata exclusively at __________ to incorporate $CO_2$ into organic acids.

night

The currently accepted structural concept that cellular membranes consist of proteins drifting individually within a fluid lipid bilayer is the __________ model.

fluid mosaic

Membranes remain fluid at lower temperatures if they are rich in phospholipids with __________ hydrocarbon tails, which have kinks that prevent tight packing.

unsaturated

In animal cell membranes, the steroid molecule __________ serves as a fluidity buffer by restraining phospholipid movement at warm temperatures and preventing tight packaging at cool temperatures.

cholesterol

The hydrophobic transmembrane regions of an integral membrane protein typically consist of stretches of nonpolar amino acids coiled into __________.

alpha helices

The passage of water molecules across plasma membranes is vastly accelerated by channel proteins called __________.

aquaporins

If an animal cell without a rigid cell wall is placed into a(n) __________ solution, water enters the cell faster than it leaves, causing the cell to lyse.

hypotonic

When a plant cell is placed in a hypertonic environment, it loses water, causing the plasma membrane to pull away from the cell wall in a lethal condition called __________.

plasmolysis

In each cycle powered by the hydrolysis of one ATP, the sodium-potassium pump exports three $Na^+$ ions out of the cytoplasm and imports __________ $K^+$ ions into the cell.

two ($2$)

In plant cotransport systems, the active transport of sucrose into the cell is coupled to the downhill diffusion of __________ previously exported by a proton pump.

protons ($H^+$)

The bulk transport mechanism where specific external ligands bind to outer membrane receptors and trigger the pinching off of coated vesicles is known as __________.

receptor-mediated endocytosis