The Fundamental Unit of Life – Practice Flashcards

These flashcards cover key discoveries, structures, organelles, processes, and distinctions related to cells—the fundamental unit of life.

Who coined the term “cell,” and in which year?

Robert Hooke in 1665, after observing cork under his self-designed microscope.

What microscopic discovery did Antonie van Leeuwenhoek make in 1674?

He observed free-living single-celled organisms in pond water.

State the original cell theory proposed by Schleiden and Schwann.

All plants and animals are composed of cells, and the cell is the basic structural and functional unit of life.

Who added the idea that all cells arise from pre-existing cells, and when?

Rudolf Virchow in 1855.

Define a unicellular organism and give one example.

An organism composed of a single cell, e.g., Amoeba (others include Chlamydomonas, Paramoecium, bacteria).

What is the main function of the plasma (cell) membrane?

It acts as a selectively permeable barrier, regulating the entry and exit of substances.

Explain diffusion with respect to cellular exchange of gases.

It is the movement of molecules like CO₂ or O₂ from a region of higher concentration to one of lower concentration across the membrane.

Define osmosis.

The net diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

What happens to an animal or plant cell placed in a hypotonic solution?

Water enters the cell by osmosis, causing it to swell.

What is plasmolysis?

The shrinking of a plant cell’s contents away from the cell wall when it loses water through osmosis.

Why is the plasma membrane described as selectively permeable?

Because it permits some substances to pass through while restricting others.

What is endocytosis, and which organism commonly uses it?

A process where a cell engulfs external material by infolding its membrane; Amoeba uses it to obtain food.

List one key structural difference between prokaryotic and eukaryotic cells.

Prokaryotes lack a true nucleus and membrane-bound organelles, whereas eukaryotes possess both.

State two primary roles of the nucleus.

(1) Houses genetic material (DNA) and directs cellular activities. (2) Controls cell reproduction by regulating cell division.

Of what are chromosomes composed?

DNA and proteins.

What are genes?

Functional segments of DNA that carry hereditary information.

Define cytoplasm.

The fluid content inside the plasma membrane that contains the cell’s organelles.

Describe the structure and role of rough endoplasmic reticulum (RER).

A membrane network studded with ribosomes; synthesises and transports proteins.

Give one major function of smooth endoplasmic reticulum (SER).

Synthesises lipids and helps detoxify poisons and drugs (also aids in membrane biogenesis).

What are the main functions of the Golgi apparatus?

Modifies, stores, and packages ER products and forms lysosomes.

Why are lysosomes nicknamed “suicide bags”?

Their digestive enzymes can destroy the cell if the lysosome bursts or leaks.

Why are mitochondria called the powerhouses of the cell?

They produce ATP (adenosine triphosphate), the cell’s main energy currency.

Name two similarities between mitochondria and chloroplasts.

Both have double membranes and possess their own DNA and ribosomes.

What are plastids, and what two main types exist?

Plant-cell organelles; chromoplasts (coloured, including chloroplasts) and leucoplasts (colourless).

State the primary role of chloroplasts.

They perform photosynthesis using chlorophyll to capture sunlight.

What do leucoplasts store?

Reserve materials such as starch, oils, or proteins.

Give two functions of the large central vacuole in mature plant cells.

Maintains turgidity/rigidity and stores important substances (e.g., sugars, amino acids, wastes).

Define mitosis.

Cell division producing two genetically identical daughter cells for growth and tissue repair.

Define meiosis.

Cell division producing four daughter cells with half the chromosome number, forming gametes.

What is ATP?

Adenosine triphosphate, the molecule that stores and supplies energy for cellular processes.

Why don’t most plant cells burst in hypotonic solutions?

Their rigid cellulose cell wall counters the inward osmotic pressure.

What is membrane biogenesis?

The formation of new cell membranes from proteins and lipids synthesised in the ER.