IMAT Biology Lesson 2.1 | The Cell | Cell Theory & Cell Size

Summary

In this lecture, Andy from Med School EU introduces cell theory and explores cell size, forming the foundation for understanding biological life. The session covers the three core principles of cell theory: all organisms are made of cells, the cell is the basic unit of life, and cells arise from pre-existing cells. It then delves into cell size, illustrating the scale from atoms and DNA to viruses, bacteria, organelles, and full plant and animal cells, highlighting units like nanometers and micrometers. The lecture also provides practical tips for IMAT exam questions, including ranking structures by size and comparing plant and animal cells.

Takeaways

• 🔬 Cell theory, proposed by Robert Hooke, is the foundation of biological science and includes three key principles.
• 🧬 All organisms are composed of one or more cells, whether unicellular or multicellular, including bacteria, plants, animals, fungi, and protists.
• 🏗️ The cell is the basic structural and functional unit of life; if a cell is damaged or broken, it loses its life functions.
• 🔁 Cells arise only from pre-existing cells through asexual or sexual reproduction; spontaneous formation from non-living matter does not occur.
• 📏 Understanding metric units (meters, millimeters, micrometers, nanometers) is essential to measure and compare cell and molecular sizes.
• ⚛️ Atoms are the smallest structures, e.g., oxygen atom is 0.07 nm, followed by DNA double helix at 2 nm, and cell membranes at 9 nm.
• 🦠 Viruses, such as HIV and influenza, are around 100 nm, making them larger than cell membranes but smaller than bacteria.
• 🧫 Bacteria like E. coli measure about 1 µm, while organelles like mitochondria range from 1–5 µm, supporting the endosymbiotic theory.
• 🧫 Animal cells typically measure 5–30 µm, whereas plant cells are larger, around 10–100 µm, often with central vacuoles for nutrient storage.
• 👁️ Human eye can see down to about 1 mm, so individual cells are too small to be seen without a microscope.
• 📚 For the IMAT exam, students need to know how to rank biological structures by size and convert between measurement units accurately.
• 🧪 Viruses are smaller than bacteria, and plant cells are generally larger than animal cells, which is important for exam comparisons.

Q & A

Who proposed the cell theory and what was his background?

The cell theory was proposed by RobertScript analysis Q&A Hooke, who was an engineer and scientist using the original microscope to study living organisms.

What are the three main tenets of cell theory?

1) All organisms are composed of one or more cells. 2) The cell is the basic structural and functional unit of all living organisms. 3) Cells arise only from pre-existing cells.

Why is the cell considered the basic structural and functional unit of life?

Because life functions such as growth, reproduction, and response to stimuli cannot occur if a cell is broken; units simpler than individual cells cannot sustain life independently.

Can cells arise spontaneously from non-living matter?

No, cells can only arise from the division of pre-existing cells through asexual or sexual reproduction.

What units of measurement are important for understanding cell size?

Meters, centimeters, millimeters, micrometers, and nanometers are important, along with the ability to convert between them.

What is the size of an oxygen atom and how does itQ&A based on script compare to a DNA double helix?

An oxygen atom is 0.07 nanometers in diameter, while a DNA double helix has a width of 2 nanometers, making the DNA much larger than a single atom.

How thick is the cell membrane and how does it compare to viruses?

The phospholipid bilayer of the cell membrane is 9 nanometers thick, while larger viruses such as HIV are about 100 nanometers, making viruses over ten times thicker than the membrane.

What is the size range of a typical mitochondrion and what evolutionary theory is associated with it?

Mitochondria are typically 1–5 micrometers in size, and the endosymbiotic theory suggests they may have evolved from free-living bacteria.

How do animal and plant cells compare in size?

Animal cells typically range from 5–30 micrometers, whereas plant cells are generally larger, averaging 10–100 micrometers.

How does the size of bacteria compare to viruses and eukaryotic cells?

Bacteria are larger than viruses but smaller than eukaryotic cells. For example, E. coli bacteria are about 1 micrometer, whereas viruses like HIV are around 100 nanometers.

Why is it important for IMAT students to understand cell sizes?

Students may be asked to rank structures from smallest to largest or vice versa, so understanding relative sizes helps answer exam questions accurately.

What is the approximate size of a human egg cell compared to a typical animal cell?

A human egg cell is about 100 micrometers, which is several times larger than a typical animal cell.