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Cell theory

Introduction to cell theory--the idea that 1) all living things are made of one or more cells, 2) cells are the basic unit of life and 3) all cells come from other cells. Explore the roles that Hooke, Leeuwenhoek and others played in developing cell theory.

Hooke and Leeuwenhoek were two of the first scientists to use microscopes to study the microscopic world of cells. Hooke coined the term "cell" after observing the tiny compartments in cork, while Leeuwenhoek discovered a variety of living creatures in pond water, blood, and other samples. They contributed to the cell theory by suggesting that cells are the fundamental units of life and structure, and that all living things consist of one or more cells that originate from other cells by division. 

Onderwerp en thema
Form 1
Biology
Cell structure and organisation
Concept of cells
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2015
Schepper/Auteur
Sal Khan
Trefwoord
Cells

Cells and organisms

All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular).

Onderwerp en thema
Form 1
Biology
Cell structure and organisation
Concept of cells
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2022
Schepper/Auteur
Khan Academy
Trefwoord
Cells

Effects of different wavelengths of radiation

When electromagnetic radiation is absorbed by a material the energy it carries has to go somewhere. When lower energy waves, like radio and infrared waves, are absorbed there can be an increase in temperature of the absorbing material. Higher energy waves, like x-ray and gamma waves, can actually permanently damage or change materials. Learn about the different types of electromagnetic waves and how their energies can influence their effects on objects.

Onderwerp en thema
Form 1
Physics
Waves
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2021
Schepper/Auteur
Sal Khan
Trefwoord
Electromagnetic Radiation
Wavelength
electromagnetic waves

Fractional Exponents to Radicals

Use the dynamic worksheet to practice simplifying expressions with fractional exponents, rewriting them as radicals.

Onderwerp en thema
Form 2
Mathematics
Exponents and radicals
Radicals
Type bron
Werkbladen en klassikale activiteiten
Taal
English
Uitgever
GeoGebra
Publicatiedatum
2019
Schepper/Auteur
Audrey McLaren
Steve Phelps
Trefwoord
Exponents
Fractional Exponents
Radicals

Introduction to the cell

Introduction to the cell.

Onderwerp en thema
Form 1
Biology
Cell structure and organisation
Concept of cells
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2017
Schepper/Auteur
Sal Khan
Trefwoord
Cells

Radicals and Rational Exponents

In this section, you will:

  • Evaluate square roots.
  • Use the product rule to simplify square roots.
  • Use the quotient rule to simplify square roots.
  • Add and subtract square roots.
  • Rationalize denominators.
  • Use rational roots.
Onderwerp en thema
Form 2
Mathematics
Exponents and radicals
Radicals
Type bron
Cursus
Taal
English
Uitgever
openstax
Publicatiedatum
2017
Schepper/Auteur
Jay Abramson
Trefwoord
Exponents
Radicals
Rational Exponents

Scale of cells

Even though molecules, proteins, viruses, and cells are all tiny, there are significant size differences between them. The diameter of a water molecule is roughly 0.28 nanometers. The diameter of the protein hemoglobin is roughly 5 nanometers. The diameter of the HIV virus is roughly 120 nanometers. A red blood cell is 6-8 micrometers.

Onderwerp en thema
Form 1
Biology
Cell structure and organisation
Concept of cells
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2015
Schepper/Auteur
Sal Khan
Trefwoord
Cells

Simplifying Radicals

Exercises requiring expressions to be re-written in 'Simple Radical Form'.

Onderwerp en thema
Form 2
Mathematics
Exponents and radicals
Radicals
Type bron
Werkbladen en klassikale activiteiten
Taal
English
Uitgever
GeoGebra
Publicatiedatum
2020
Schepper/Auteur
Courtenay Fullerton
Tim Brzezinski
Trefwoord
Exponents
Radicals

Wave interference

An explanation of wave interference and solution of a few examples to find the value of the total wave when two wave pulses overlap

Onderwerp en thema
Form 1
Physics
Waves
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2016
Schepper/Auteur
David SantoPietro
Trefwoord
Waves
Wavelength
Wave Interference
Mechanical Waves
Mechanical Sounds

Wave Properties

The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing.

Onderwerp en thema
Form 1
Physics
Waves
Type bron
Video
Taal
English
Uitgever
Khan Academy
Publicatiedatum
2021
Schepper/Auteur
Khan Academy
Trefwoord
Waves
Wavelength