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GRADE 11 LIFE SCIENCES
SESSION 5: HUMAN NUTRION
Key Concepts
In this session we will focus on summarising what you need to know about:
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The differences in dentition between herbivores, carnivores and omnivores,
specifically in terms of the nutritional requirements and energy relationships
Identification of the macro-structure of alimentary canal and associated
organs and the functions of the different parts
Processes of ingestion, digestion, absorption, assimilation and egestion
Terminology & definitions
Nutrition
Metabolism
Autotrophs
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Intake and use of food in metabolism
All chemical reactions that take place in a cell
an organism which is able to produce its own organic food by
photosynthesis e.g. plants
Heterotrophs
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an organism that is dependent on another organism for food
Ingestion
Digestion
Absorption
Assimilation
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Deamination
Homeostasis
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Insulin
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Glucagon
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Diabetes
Malnutrition
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Bolus
Chyme
Peristalsis
Villus
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Hydrolases
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intake of food (eat)
large molecules of food are broken down to small molecules
the small molecules are absorbed into the blood
Absorbed nutrients are taken in the blood plasma to all body
cells
Removal of the amino group from and amino acid in the liver
A series of processes by which the internal environment of the
body is kept constant e.g. sugar
Hormone secreted by the pancreas that converts glucose to
glycogen
Hormone secreted by the pancreas that converts glycogen to
glucose
Disease characterised by high blood sugar
A physical or psychological disorder that is usually the result of a
faulty or inadequate diet
A ball of food particles which stick together because of saliva
Partially digested, finely divided food which leaves the stomach
Wavelike movement in the tubes of the alimentary canal
Tiny finger like projections of the small intestine that absorb the
digested food
Enzymes that break down food chemically e.g. carbohydrase,
proteases and lipase
Key Concepts
X-planation
All living organisms need nutrition of some sort in order to obtain the energy and
building blocks required to sustain life, growth and development.
Autotrophic organisms (green plants for
example) use photosynthesis to obtain their
nutrients and energy, while heterotrophic
organisms (e.g. humans) need to consume
food in order to obtain the nutrients and
energy they require.
For a human being to be healthy the
nutrients required must be consumed in the
correct proportions and amounts –this type of
diet leads to maximum health and strength,
while an unbalanced diet can cause many
health problems. If the incorrect proportions
or amounts of nutrients are eaten for
prolonged periods of time the result is malnutrition.
Different teeth for different life styles
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Different animals have different types of teeth depending what they eat.
Because mammals are endothermic they need a lot of food to produce heat
energy to keep their bodies warm. For this they need specialised teeth to help
them digest their food properly
Mammals usually have four different types of teeth:
o Incisors – biting food
o Canines – catching, holding, tearing or killing
o The premolars and molars – crushing and grinding
Herbivores
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Well-developed incisors –for clipping off plant material
Usually No canines
Premolars and molars are broad and flat for chewing
There is a space in front of the premolars called the diastema. The animal
pushes its tongue through this gap to sweep grass into its mouth
Sheep
0:0:3:3
3:1:3:3
I C P M
32 teeth
Carnivores
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Canines long for piercing skin and tearing and killing prey.
Incisors short and pointed for holding and shredding
Premolars and molars have jagged edges that slice, they are called carnassial
teeth
Cat
3:1:3:1
3:1:2:1
I C P M
30 teeth
Omnivores
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Incisors shovel shaped for biting
Canines pointed for tearing
Flat molars for grinding food
The Digestive System
Ingestion
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this is where food is taken in to the alimentary canal
Digestion
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this is where large insoluble molecules of food are broken down to small
molecules
digestion is physical and chemical
Physical
o During this process food is broken down into smaller particles to
enlarge the outer surface area for enzyme action during chemical
digestion. This includes chewing, bolus formation, churning movements
and peristalsis.
Chewing
Mastication - Food is broken down in smaller pieces by
the teeth and the tongue.
Bolus formation
After food has been chewed it is rolled into a ball, bolus,
and swallowed down the pharynx into the oesophagus.
Churning movements
Takes place by muscular contractions in the stomach
wall. Food is also mixed with the gastric juice in which
digestive enzymes occur
Peristalsis
Muscular contractions of the wall of the alimentary canal,
which develop by the contraction and relaxation of the
circular and longitudinal muscles. This helps push the
food through the alimentary canal.
Chemical Digestion
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This is the breakdown of large insoluble molecules to smaller soluble
molecules by hydrolases (enzyme) by a process called hydrolysis.
During hydrolysis water id added.
Substrate
Carbohydrates
Proteins
Fats / lipids
Enzyme
Where is it
produced?
Carbohydrases
In the mouth,
e.g. salivary amylase pancreas and small
maltase
intestines
sucrase
lactase
Proteases
In the stomach and
e.g.pepsin
pancreas and small
rennin
intestine
trypsin
erepsin
Lipase
In the pancreas
and small intestine
End product
Glucose
Fructose
Galactose
Amino acids
Glycerol and fatty
acids
ABSORBTION
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Digested food is now in soluble form (glucose, amino acids, glycerol and fatty
acids) and is absorbed by diffusion by the villi that line the small intestine.
Structure and importance of a villus
- The villus is surrounded by a single thin layer of columnar epithelium
for fast and easy diffusion
- The villus contains many capillary blood vessels for effective uptake of
nutrients
- It contains a central lacteal for the uptake of fats
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Goblet cells in columnar epithelial secrete mucous to dissolve digested
nutrients
The columnar epithelial cells have many mitochondria, which provide
energy for active transport
Microvilli on the columnar epithelium enlarge the absorption area
Most absorption in the small intestine occurs in the
jejunum. The products of digestion enter cells of the villi,
move across the cells, and enter blood vessels called
capillaries. Diffusion accounts for the movement of many
nutrients, but active transport is responsible for the
movement of glucose and amino acids. The products of fat
digestion pass as small droplets of fat into lacteals, which
are branches of the lymphatic system.
Absorption is completed in the final part of the small
intestine, the ileum. Substances that have not been
digested or absorbed then pass into the large intestine.
All substances that are absorbed end up passing through
the liver, carried away from the gut by the hepatic portal
system.
THE HEPATIC PORTAL SYSTEM
Once inside the blood vessels the nutrients are transported to the liver via the
hepatic portal vein (part of the hepatic portal system, which includes the veins
draining blood from the stomach and the intestines). In the liver many nutrients are
processed before moving on to the cells of the body via the hepatic vein
THE ROLE OF THE LIVER
Excess Nutrients
The cells of the liver remove excess glucose from
the bloodstream and convert the glucose to a
polymer called glycogen for storage.
The liver also functions in amino acid metabolism.
In a process called deamination, it converts some
amino acids to compounds that can be used in
energy metabolism.
In doing so, the liver removes the amino groups
from amino acids and uses the amino groups to
produce urea. Urea is removed from the body in the
urine. Fats are processed into two-carbon units that
can enter the Krebs cycle for energy metabolism.
The liver also stores vitamins and minerals, forms many blood proteins,
synthesizes cholesterol, and produces bile for fat digestion.
Toxins
Alcohol, drugs and other materials that may be harmful to the human body are
detoxified by the liver and rendered harmless. Other organs are responsible for the
excretion of these products e.g. urea from excess amino acid metabolism is excreted
by the kidneys.
X-ample Questions
Question 1
Study diagram 1 and answer the questions that follow
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Diagram 1.: Diagram showing a part of the digestive system
1.1
Provide labels 1-6.
1.2
What is the food in the part labelled 2 known as?
(1)
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Draw a suitable graph to show the pH of the mouth,
stomach, and small intestine. (6)
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1.3
(6)
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Study diagram 2 and answer the questions that follow.
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1.4
Name blood vessel 1 and the valve labelled 4.
(2)
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1.5
The pancreas labelled 5 is an endocrine as well as an
exocrine gland. Name one endocrine function of the
pancreas.
(2)
1.6
In which part would you experience heart burn?
Explain what heartburn is.
(1)
(2)
1.7
Draw a villus and label the relevant structures.
( 2 mark drawing, 1 mark heading, 7 labels)
(10)