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Higher Human Biology
Unit 1
Human Cells
KEY AREA 8: Energy Systems
Human Cells Learning Intentions
KEY AREA 8 – Energy Systems
1. Energy Systems in muscle cells
2. Lactic Acid Metabolism (Anaerobic Respiration)
3. Types of Skeletal Muscle Fibres
8a) Energy Systems in muscle cells
ATP is the source of immediately-available chemical energy required for muscular
contraction
During intense muscular activity, muscle cells break down ATPADP + Pi + energy
Each muscle only stores sufficient ATP for a few contractions
Energy needed for repetitive muscular contraction comes from a chemical called creatine
phosphate
During strenuous muscular activity, creatine phosphate in muscle cells breaks down,
releasing energy and phosphate, which is used to convert ADP to ATP by phosphorylation
Creatine phosphate system can only support strenuous muscle activity for around 10
seconds, and then the creatine phosphate supply runs out.
Creatine phosphate is restored when energy demands are low
8b) Energy Systems in muscle cells
Creatine Phosphate System
8c) Lactic Acid Metabolism (Anaerobic Respiration)
After 10seconds of intensive exercise creatine phosphate store is depleted and if
the intensive exercise continues the cells start to respire anaerobically because they
do not receive an adequate supply of oxygen from the blood for aerobic respiration
During Anaerobic Respiration, the only stage of respiration that can occur is
Glycolysis
In Glycolysis in Anaerobic Respiration
Glucose  Pyruvate Lactic Acid
This conversion involves the transfer of hydrogen from NADH
NAD is regenerated
Lactic Acid gathers in muscle cells and causes fatigue and an oxygen debt builds up
The oxygen debt gets repaid when exercise comes to a halt, and energy made from
Aerobic Respiration is used to convert lactic acid back to pyruvic acid and glucose
8d) Lactic Acid Metabolism (Anaerobic Respiration)
8e) Types of Skeletal Muscle Fibres
Body movements are brought about by the action of skeletal muscle fibres
Skeletal muscle fibres fall into two categories based on the duration of their twitches
Type 1 (Slow-twitch muscle fibres)
Type 2 (Fast-twitch muscle fibres)
Feature
Type 1 Slow-Twitch
Type 2 Fast-Twitch
Muscle contraction speed
Slow
Fast
Length of time for which contraction
lasts
Long
Short
Speed at which fibre becomes fatigued
Slow
Fast
Respiratory Pathways to make ATP
Aerobic Respiration
Glycolysis
Number of mitochondria
Many
Few
Blood supply
Large
Small
Concentration of myoglobin in cells
High concentration
Low concentration
Storage fuels used
Fats
Glycogen/Creatine
phosphate
Activities
Long distance running,
skiing
Sprints, Weightlifting
Human Cells Questions
KEY AREA 8 – Energy Systems
1. Testing Your Knowledge 2
Page 116
2.
Page 117
What You Should Know
3. Quick Quiz
Q’s 1-4