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AQA GCSE Biology 9-1 > (Paper 1) 2.2 Organisation: The Digestive System > Flashcards

(Paper 1) 2.2 Organisation: The Digestive System Flashcards

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1
Q

What is the main function of the digestive system?

A

To break down large, insoluble food molecules into smaller, soluble ones that can be absorbed into the bloodstream.

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2
Q

What is digestion?

A

The process of breaking down food into smaller molecules that the body can absorb and use.

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3
Q

What are the two types of digestion?

A

Mechanical digestion –

  1. physical breakdown (e.g. chewing)
  2. Chemical digestion – using enzymes to break down food
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4
Q

Where does digestion begin?

A

In the mouth.

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5
Q

What is the role of the mouth in digestion?

A

Chewing (mechanical digestion) and mixing with saliva containing amylase (chemical digestion of starch).

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6
Q

What is the function of the oesophagus?

A

To transport food from the mouth to the stomach using muscular contractions (peristalsis).

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7
Q

What happens in the stomach?

A

Food is mixed with acid (hydrochloric acid) and enzymes to digest proteins, strong muscular walls churn food.

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8
Q

What does the small intestine do?

A

It’s where most digestion and absorption of nutrients takes place

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9
Q

What are the three major macronutrients in food?

A

Carbohydrates, proteins, and lipids (fats).

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10
Q

Why must carbohydrates, proteins, and lipids be broken down before absorption?

A

Because they are too large to pass through the gut wall.

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11
Q

Why are broken-down nutrients reassembled in the body?

A

To build human-specific molecules, not plant or animal versions from food.

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12
Q

What is the main function of carbohydrates?

A

To provide energy; glucose is the main respiratory substrate.

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13
Q

Name some sources of starch.

A

Potatoes, rice, wheat products, bread, cereals, pasta.

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14
Q

Name some sources of sugar.

A

Fruit, smoothies, fizzy drinks, chocolate, sweets.

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15
Q

Name 3 types of sugar molecules in the modern diet

A

fructose, sucrose, and glucose

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16
Q

What is the main function of proteins?

A

Growth and repair.

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17
Q

Name some protein-rich foods.

A

Meat, eggs, cheese, beans, nuts, seeds.

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18
Q

What are the main functions of lipids?

A

Energy storage and forming part of cell membranes.

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19
Q

Name some sources of lipids.

A

Butter, margarine, meat, plant oils, oily fish, nuts, seeds.

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20
Q

What are the two main types of carbohydrates in our diet?

A

Sugars and starches.

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21
Q

What is the basic unit of carbohydrates?

A

Glucose

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22
Q

What is starch made of?

A

It is a polymer of glucose.

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23
Q

Why must starch be broken down in digestion?

A

It is too large to pass through the gut wall.

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24
Q

What is cellulose and why can’t we digest it?

A

A polymer of glucose found in plant cell walls; it cannot be broken down by our digestive enzymes.

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25
What happens to glucose after absorption?
It is used for respiration or converted into glycogen for storage.
26
What are proteins made of?
amino acids
27
Why must proteins be digested?
They are too large to pass through the gut wall.
28
What happens to amino acids after absorption?
They are reassembled into proteins by the body (protein synthesis).
29
Where are excess amino acids broken down?
In the liver
30
What are lipids made of?
Fatty acids and glycerol (they are esters).
31
Why must lipids be digested?
They are too large to pass through the gut wall.
32
What happens to lipids after digestion and absorption?
They are reassembled into the specific lipids needed by cells, e.g. for cell membranes.
33
What is Benedict's solution used to test for?
Reducing sugars, such as glucose.
34
What must you do to carry out Benedict's test?
Add Benedict’s solution to the food sample and heat it in a water bath for a few minutes.
35
What is a positive result for Benedict’s test?
A colour change from blue to green, yellow, orange, red or brown depending on the amount of sugar.
36
What hazard is associated with Benedict’s solution?
It is an irritant – wear safety goggles and avoid skin/eye contact.
37
What is iodine solution used to test for?
Starch
38
What is a positive result for starch?
The sample turns blue-black.
39
What hazard is associated with iodine solution?
It is an irritant – wear safety goggles and avoid contact with skin and eyes.
40
What is the Biuret test used for?
To test for proteins.
41
What is a positive result for the Biuret test?
The solution turns purple/lilac.
42
What hazards are associated with Biuret solutions?
Biuret A: Corrosive Biuret B: Irritant Always wear safety goggles.
43
What is the Sudan III test used for?
To test for lipids (fats and oils).
44
What is a positive result for the Sudan III test?
A red layer forms on top of the solution.
45
Why is Sudan III a hazard?
It is flammable (dissolved in alcohol); wear goggles, avoid contact with skin/eyes.
46
What is an alternative test for lipids?
The emulsion test, using ethanol.
47
What is a positive result for the emulsion test?
A milky-white emulsion forms.
48
Why is ethanol a hazard in the emulsion test?
It is flammable – wear goggles, avoid heat/flames.
49
What is the function of the mouth in digestion?
Begins the digestion of carbohydrates using amylase in saliva.
50
What is the main digestive role of the stomach?
Begins the digestion of proteins; small molecules like alcohol may be absorbed.
51
What happens in the duodenum (first part of the small intestine)?
Continues the digestion of carbohydrates and proteins; begins the digestion of lipids.
52
What happens in the ileum (second part of the small intestine)?
Completes digestion and absorbs single sugars, amino acids, fatty acids, and glycerol.
53
What is the role of the large intestine?
Absorbs water and egests undigested food.
54
What do digestive enzymes do?
Break down large, insoluble food molecules into small, soluble ones for absorption.
55
What structures increase the surface area of the small intestine for absorption?
Villi (on the intestinal wall) Microvilli (on epithelial cells)
56
What is the role of villi in absorption?
Increase surface area and absorb nutrients like sugars and amino acids into the blood.
57
What are lacteals, and what do they absorb?
Vessels in villi that absorb fatty acids and glycerol (digested lipids).
58
After absorption, where is most digested food transported?
To the liver, via the bloodstream.
59
What are enzymes?
Biological catalysts that speed up chemical reactions without being used up.
60
Why are enzymes essential in digestion?
They break down large, insoluble molecules (carbohydrates, proteins, lipids) into smaller, soluble ones for absorption.
61
What is the active site of an enzyme?
The region where the substrate binds to the enzyme.
62
What is the lock and key theory?
Each enzyme's active site has a unique shape that only fits a specific substrate—like a key fits a lock.
63
Are enzymes reusable?
Yes, they are not used up in reactions.
64
What are enzymes made of?
Proteins, which are made of folded chains of amino acids.
65
What holds the enzyme’s shape together?
Weak forces between amino acids in the protein chain.
66
What happens to enzyme activity at low temperatures?
It slows down due to reduced molecular movement and fewer collisions.
67
What is the optimum temperature for human enzymes?
Around 37°C
68
What happens if the temperature is too high?
The enzyme becomes denatured – the active site changes shape and no longer fits the substrate.
69
How does pH affect enzyme activity?
pH changes can alter the enzyme's shape by affecting the charges on amino acids, which changes the active site.
70
What happens to an enzyme at an extreme pH?
It becomes denatured—the change is usually permanent.
71
What is the optimum pH range for most cellular enzymes?
pH 7.0 – 7.4
72
What is the optimum pH for salivary amylase?
pH 6.8
73
What is the optimum pH for stomach protease (pepsin)?
pH 1.5 – 2.0
74
What is the optimum pH for pancreatic protease (trypsin)?
pH 7.5 – 8.0
75
How is low pH maintained in the stomach?
By the secretion of hydrochloric acid.
76
How is high pH maintained in the duodenum?
By the release of sodium hydrogencarbonate from the pancreas
77
What are the three main types of digestive enzymes?
Carbohydrases, proteases, and lipases.
78
What is the role of digestive enzymes?
To break large, insoluble molecules into small, soluble ones for absorption.
79
What do carbohydrases break down?
Carbohydrates (e.g. starch into sugars).
80
Which enzyme breaks down starch?
Amylase
81
Where is salivary amylase produced and what does it do?
Produced in salivary glands, breaks down starch into maltose in the mouth.
82
Where is pancreatic amylase produced and what does it do?
Produced in the pancreas, breaks down starch into maltose in the duodenum.
83
What does amylase in the ileum do?
Breaks down maltose into glucose.
84
What do proteases break down?
Proteins into amino acids.
85
Where is pepsin produced and where does it act?
Produced in the stomach (gastric glands); begins protein digestion into amino acids.
86
Where is trypsin produced and where does it act?
Produced in the pancreas; continues protein breakdown in the duodenum.
87
What does peptidase do in the ileum?
Completes protein digestion by breaking peptides into amino acids.
88
What do lipases break down?
Lipids (fats) into fatty acids and glycerol.
89
Where is lipase produced and where does it act?
Produced in the pancreas; acts in the duodenum.
90
Does the liver produce digestive enzymes?
No, it produces bile, but not enzymes.
91
What is the main digestive role of the liver?
Producing bile, which aids in the digestion of lipids.
92
Where is bile stored and concentrated?
In the gall bladder.
93
What does bile do to lipids?
Emulsifies them – breaks them into tiny droplets to increase surface area for lipase action.
94
Why is emulsification important?
It increases the surface area of fats, making them easier for lipase to break down.
95
What pH condition does bile help create in the small intestine?
A slightly alkaline pH (neutralises stomach acid).
96
Why must stomach acid be neutralised in the small intestine?
To create the optimum pH for pancreatic enzymes to function effectively.

AQA GCSE Biology 9-1 (29 decks)

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