IELTS Academic Reading Practice 16

 
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This reading practice simulates one part of the IELTS Academic Reading test. You should spend about twenty minutes on it. Read the passage and answer questions 1-11.

Questions 1-6

The reading passage has six paragraphs labelled A-F.

Which paragraph contains the following information?

Write the correct letter A-F in boxes 1-6 on your answer sheet.

NB You may use any letter more than once.

1 An example of how proteins convey information inside a cell
2 A reference to how a specific area of study is sometimes passed over
3 An account of how particular molecules work at preventing hardening
4 description of how cells remain nourished
5 An explanation of how the outer layer of a cell prevents the ingress of other substances
6 An outline describing how molecules move
Questions 7-11

Complete the sentences below.  

Choose NO MORE THAN THREE WORDS from the passage for each answer.
Write your answers in 7-11 on your answer sheet.

The tails of phospholipids are known as .

Proteins assist in making the membrane .

Some proteins are responsible for communication.

proteins are selective when attaching themselves to molecules.

At cholesterol slows down solidification.


Answer Sheet
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  • help Learn how to HIGHLIGHT & ADD NOTES
    1. HOLD LEFT CLICK
    2. DRAG MOUSE OVER TEXT
    3. RIGHT CLICK SELECTED TEXT

Cell Membranes

A The human body is made up of millions of cells, which are the little building blocks of life. Each cell contains many functional subunits (organelles) that enable its proper functioning. Cells are protected from the external environment by a cell membrane. While the structure and function of organelles are extensively covered in various biology courses, the importance of the study of cell membranes is often overlooked. This article provides a short introduction into the basic functions and anatomy of a cell membrane.

B Cell membranes protect and organize cells. Most importantly they serve as barriers, protecting the cell’s interior from the environment outside. Because cells always exist in watery environments, their membranes should be structured not to dissolve in water. This function carried out by special chemical molecules, known as phospholipids. Phospholipids have tails made up of 2 molecules of fat that ‘avoid’ water, and heads that have an affinity for water. Phospholipid tails are called hydrophobic, which means “water fearing”, and heads called “hydrophilic”, meaning “water loving.”  When phospholipids are added to water, they self-assemble into double-layered structures, shielding their hydrophobic portions from water and exposing their hydrophilic portions to the environment. This phospholipid bilayer can be thought of similarly to a sandwich, where phospholipid heads are bread rolls and tails are the sandwich filling.

C In addition to lipids, membranes are loaded with proteins. They usually go through the lipid bilayer and are exposed to both a watery environment as well as a cell's interior. In fact, proteins account for roughly half the mass of most cellular membranes. They make the membrane semi-permeable, which means that some molecules can cross the lipid bilayer, while others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly. On the other hand, cell membranes restrict diffusion of highly charged molecules, such as ions, and large molecules, such as sugars and amino acids. The passage of these molecules relies on specific transport proteins within the cell membrane.

D Membrane transport proteins are specifically selective to the molecules which they help transport, often using energy to aid in passage. They may also need to move nutrients against a higher concentration of particles, which requires additional energy. To maintain the health of a cell, it is vital to maintain the balance of particles, known as concentration gradients, as well as to be able to occasionally move materials against them. Thanks to membrane barriers and transport proteins, the cell can gather nutrients in higher concentrations than there are in the natural environment and, conversely, dispose of waste products.

E Other membrane-embedded proteins have communication-related jobs. From outside the cell, an area known as the extracellular environment, large molecules such as hormones or immune mediators, bind to the receptor proteins on the cell membrane. Such binding causes changes in the shapes of proteins which transmit signals to messenger molecules within cells. Like transport proteins, receptor proteins are specific and selective when binding to molecules.

F Other important components in a cell membrane are cholesterol molecules, which account for about 20 percent of the lipids in animal cell plasma membranes. However, cholesterol is not present in bacterial membranes or mitochondrial membranes. The cholesterol molecules are embedded in place of phospholipid molecules and help to regulate the stiffness of membranes. To function properly, the cell membrane should be in a fluid (non-solid) state. Cholesterol reduces membrane fluidity at moderate temperatures by reducing the movement of phospholipids. But at low temperatures, it slows down solidification by disrupting the regular packing of phospholipids.

Reading Passage Vocabulary
Cell Membranes

A The human body is made up of millions of cells, which are the little building blocks of life. Each cell contains many functional subunits (organelles) that enable its proper functioning. Cells are protected from the external environment by a cell membrane. While the structure and function of organelles are extensively covered in various biology courses, the importance of the study of cell membranes is often overlooked. This article provides a short introduction into the basic functions and anatomy of a cell membrane.

B Cell membranes protect and organize cells. Most importantly they serve as barriers, protecting the cell’s interior from the environment outside. Because cells always exist in watery environments, their membranes should be structured not to dissolve in water. This function carried out by special chemical molecules, known as phospholipids. Phospholipids have tails made up of 2 molecules of fat that ‘avoid’ water, and heads that have an affinity for water. Phospholipid tails are called hydrophobic, which means “water fearing”, and heads called “hydrophilic”, meaning “water loving.”  When phospholipids are added to water, they self-assemble into double-layered structures, shielding their hydrophobic portions from water and exposing their hydrophilic portions to the environment. This phospholipid bilayer can be thought of similarly to a sandwich, where phospholipid heads are bread rolls and tails are the sandwich filling.

C In addition to lipids, membranes are loaded with proteins. They usually go through the lipid bilayer and are exposed to both a watery environment as well as a cell's interior. In fact, proteins account for roughly half the mass of most cellular membranes. They make the membrane semi-permeable, which means that some molecules can cross the lipid bilayer, while others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly. On the other hand, cell membranes restrict diffusion of highly charged molecules, such as ions, and large molecules, such as sugars and amino acids. The passage of these molecules relies on specific transport proteins within the cell membrane.

D Membrane transport proteins are specifically selective to the molecules which they help transport, often using energy to aid in passage. They may also need to move nutrients against a higher concentration of particles, which requires additional energy. To maintain the health of a cell, it is vital to maintain the balance of particles, known as concentration gradients, as well as to be able to occasionally move materials against them. Thanks to membrane barriers and transport proteins, the cell can gather nutrients in higher concentrations than there are in the natural environment and, conversely, dispose of waste products.

E Other membrane-embedded proteins have communication-related jobs. From outside the cell, an area known as the extracellular environment, large molecules such as hormones or immune mediators, bind to the receptor proteins on the cell membrane. Such binding causes changes in the shapes of proteins which transmit signals to messenger molecules within cells. Like transport proteins, receptor proteins are specific and selective when binding to molecules.

F Other important components in a cell membrane are cholesterol molecules, which account for about 20 percent of the lipids in animal cell plasma membranes. However, cholesterol is not present in bacterial membranes or mitochondrial membranes. The cholesterol molecules are embedded in place of phospholipid molecules and help to regulate the stiffness of membranes. To function properly, the cell membrane should be in a fluid (non-solid) state. Cholesterol reduces membrane fluidity at moderate temperatures by reducing the movement of phospholipids. But at low temperatures, it slows down solidification by disrupting the regular packing of phospholipids.

 
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