Biology Lecture Notes: Cell Structure, Enzymes, and Osmosis

This set of flashcards covers key concepts in biology including cell structures, specialization of sperm cells, enzyme function and kinetics, transport mechanisms (osmosis and active transport), and specific core laboratory practicals involving microscopy, pH, and potato tissue mass change.

What distinguishes eukaryotic cells from prokaryotic cells?

Eukaryotes have a membrane-bound nucleus and organelles (e.g. mitochondria), while prokaryotes have no nucleus and store DNA as circular loops/plasmids.

What is the function of mitochondria?

Mitochondria are the site of aerobic respiration, which releases energy ($ATP$) for cellular processes.

What is the formula for magnification?

$\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}$ ($M = \frac{I}{A}$).

What is the function of the acrosome in a sperm cell?

It contains digestive enzymes to penetrate the egg coat.

What is the role of the haploid nucleus in a sperm cell?

It contains $23$ chromosomes to combine with the egg at fertilization.

What is the function of the tail (flagellum) in a sperm cell?

It is used for swimming toward the egg.

Why is the midpiece of a sperm cell packed with mitochondria?

To release energy for movement.

How do extreme pH or high temperatures cause enzyme denaturation?

They alter the active site shape so the substrate no longer fits, and the lock-and-key fit is lost.

What is active transport?

The movement of particles against a concentration gradient (low to high) requiring energy ($ATP$) from respiration.

What is osmosis?

The net movement of water molecules from a higher to lower water concentration across a partially permeable membrane.

Which three factors affect enzyme activity?

Temperature, pH, and substrate concentration.

What are the steps to focus a light microscope slide?

Start with the lowest power objective lens, use the coarse focus wheel until the stage is just below the lens, look through the eyepiece while adjusting the coarse focus, and then use the fine focus wheel until the image is crystal clear.

What is the conversion for $1$.$0\,mm$ into micrometres ($\mu m$)?

$$1,000\,μm$$

What is the conversion for $1$.$0\,μm$ into nanometres ($nm$)?

$$1,000\,nm$$

Why must onion skin be thin when preparing a microscope slide?

To allow light to pass through the specimen.

Why is iodine stain added to cell specimens in microscopy?

It stains cell structures, such as nuclei, so they become visible under light.

What is the formula for total magnification?

$$\text{Total Magnification} = \text{Eyepiece Lens Magnification} \times \text{Objective Lens Magnification}$$

In the amylase practical, why is a water bath used?

To control temperature as a constant variable, ensuring pH is the only variable changing.

How can you tell when starch is completely broken down by amylase using iodine?

The iodine stays orange/brown and stops turning blue/black when added to the mixture.

What is the formula for the rate of an enzyme reaction?

$$\text{Rate} = \frac{1000}{\text{Time taken (s)}}$$

Why are amylase and buffer solutions pre-heated in a water bath before mixing?

To ensure both solutions reach the target temperature before the reaction starts.

What is a main source of error in iodine spot testing and how can it be improved?

Long sampling intervals (e.g., every $30\,s$) are a source of error; this can be improved by sampling every $10\,s$ or using a colorimeter.

Why are potato strips blotted dry before they are weighed in the osmosis practical?

To remove excess surface water so it does not artificially inflate the initial or final mass readings.

What is the formula for percentage mass change?

$$\text{Percentage Change} = \frac{\text{Final Mass} - \text{Initial Mass}}{\text{Initial Mass}} \times 100$$

What does the X-intercept represent on a graph of % Mass Change vs Concentration?

The point of $0\%$ mass change, representing the sucrose concentration isotonic to the potato cytoplasm.

Why is percentage change in mass calculated instead of actual mass change?

Potato strips have different starting masses, and percentage change allows for a fair comparison.

What happens to potato tissue placed in pure water?

It gains mass and becomes turgid because water moves into cells by osmosis down a water potential gradient.

What happens to potato tissue placed in a concentrated sucrose solution?

It loses mass and becomes flaccid/plasmolysed because water moves out of the cells by osmosis.