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This question group is public and is used in 28 tests.

Author: szeiger
No. Questions: 5
Created: Oct 30, 2015
Last Modified: 3 years ago

Science Cell Transport Diffusion and Osmosis

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Cells constantly need to move materials back and forth across their membranes. These substances may include salts, water, glucose, and waste products. Cells always want to maintain a constant internal environment. However, at times, there is an accumulation of materials on one side or the other of the cell membrane that needs to equal out. When this happens, a concentration gradient is formed. Usually materials flow down their concentration gradients, from high to low. This is a passive process that does not use energy. Water and oxygen are two substances that can flow into and out of a cell whenever they need to.

There are a few instances when molecules need to move up their concentration gradients. Like going up a steep hill, this process takes energy. Active transport, as this process is known, often involves ions moving back and forth across the cell membrane (i.e. the Sodium/Potassium pump of nerve cells).

Facilitated diffusion is when molecules are still traveling down their concentration gradients, but they need some help. Like regular diffusion, this process does not require any energy, but needs the involvement of some other kind of molecule to help move the gradient to equilibrium. A lot of times these "helper molecules" are called carrier proteins, which are found engrained within the cell membrane.

Other times, particles are too large to fit through the openings in the cell membrane but they still need to get inside. When this happens, cells use a transport mechanism called endocytosis (taking in) or exocytosis (pushing out) to move the materials across the membrane (see the diagram for a model of endocytosis).
Endocytosis With Text Labels
Grade 10 Simile CCSS: CCRA.R.4, RI.9-10.4
A.
A simile is a comparison that uses like or as. The author of this passage uses a simile to:
  1. explain the difference between endocytosis and exocytosis
  2. compare the process of diffusion to a household product
  3. describe the energy molecules needed to move up concentration gradients
  4. help the reader connect with the main idea of the passage
Grade 10 Context Clues CCSS: CCRA.R.4, RI.9-10.4, RST.9-10.4
B.
ACTIVE TRANSPORT, as used in the passage, can best be defined as:
  1. the process of moving molecules up concentration gradients
  2. the movement of molecules down concentration gradients
  3. the tiny holes found within concentration gradients
  4. the ability of water to pass through concentration gradients
Grade 10 Text Elements CCSS: CCRA.R.7, RI.9-10.7, RST.9-10.7
C.
Which choice best explains why the author included the diagram at the end of the passage?
  1. to show three different parts of diffusion
  2. to help readers visualize the process of endocytosis
  3. to give readers a picture of a concentration gradient
  4. to describe what happens during phagocytosis
Grade 10 Text Elements CCSS: CCRA.R.5, RI.9-10.5, RST.9-10.5
E.
Which choice BEST describes how the author organizes the passage?
  1. cause and effect
  2. definition and description
  3. compare and contrast
  4. problem and solution