BIOL10004 Lecture Notes - Plant Cell, Body Fluid, Starch
Lecture 18 - What, Why and How of Digestion
Wednesday, 2 May 2018
Main Questions:
- Why don't lions need to eat vegetables?
- Why do zebras survive on grass?
- Why do pandas (bears) eat plants?
Getting Nutrients
Plants
Autotrophs
• Require only inorganic compounds absorbed from the environment
to make organic compounds
• Use solar energy (photosynthesis) to synthesise complex organic
compounds for growth
• Do’t eed to eat aythig – photosynthesis everything they need
Animals
Heterotrophs
• Can't synthesise organic compounds from inorganic molecules need
to ingest them (hence have to consume nutrients we fundamentally
need to survive)
What do animals need?
Organic compounds – provide chemical energy
3 Classes of Organic Compounds Consumed
• Animals classed on diet of these compounds
Carbohydrates
Sugars, Starch and fibre
Main energy source
Lipids
Eg. fats
Energy & structural component of cells
High density, lots of energy
Protein
Proteins alone + amino
acids
Energy
Amino acids for protein synthesis
(enzymes, structural components of
cells, etc)
By product we need to excrete - urea
Other – essential: things we need but cannot produce ourselves; depends on species
Tables 26.1, 26.2
• Essential amino acids – nine in humans
• Essential fatty acids – only 2 in humans (omega 3 and 6)
• Vitamins – organic elements essential for metabolism
o Micronutrients: 13 vitamins essential
• Minerals – inorganic elements essential for metabolism
o 9 minerals known as trace elements
• Water – body fluid
Vitamins and minerals – important for processes such as enzyme parts, antioxidants, vitamins D (conditional bc get
some from sunlight; also digest), B, C
find more resources at oneclass.com
find more resources at oneclass.com
How much food does an animal need?
• Depends on metabolic rate, age, reproductive state, behaviour, lifestyle
o Growing phase – putting on body weight, muscle & bone density – a lot of food needed
o Pregnant – high consumption of food and nutrients
• Metabolic rate – depends on activity, body mass, environmental conditions (cold room- more energy to be
converted to keep warm for homeostasis than if in hot or optimal conditions; how we interact with
environment dictates how we control our homeostatic mechanisms)
• Type of food and ability to digest it – what do we eat, and how much can we get from it and digest and
actually utilise (different organisms have different systems of doing this – some efficient; some inefficient)
o Type of food dictates how much and how often we need to eat
▪ Eg. Food you do’t eed uh of eg. donuts) for sugar and energy or if you eat paddock of
grass (cow)
Metabolic Rate
• Size – plays a big role in metabolic rate
• Big animals need more energy than small ones (eg. Elephant needs more food than small animal)
• BUT per unit body mass – small animals need more energy
• Small animals – need more food per unit body mass and/or more energy rich food
o Eg. Hummingbird has one of the fastest metabolic rate in nature – need energy rich foods in terms
of nectar + drink at least 1/3rd body weight every day to survive
Mass-specific metabolic rate
Mouse-Elephat Cue
• Plots daily energy expenditure vs body mass – metabolic rate in terms of activity and body mass
• Named b/c of size different between mouse and elephant
• Elephant – does’t euie uh eegy pe uit ass altho oeall euies a lot
• Shrew – tiny in weight; always active; high metabolic rate therefore needs a lot of energy per unit mass
What is digestion?
• Breakdown of large molecules into smaller ones
o Must have molecules small enough and processes built into physiology to absorb nutrients into gut
to provide energy
• Eventually molecules are small enough to be absorbed across gut wall to provide energy
find more resources at oneclass.com
find more resources at oneclass.com
How?
- Mechanical digestion – teeth, grinding things down and breaking down food, stomach is heavy in terms of
muscles – constantly churning and moving food to break down food, digestive system in general is a
muscular structure
- Enzymatic digestion- specific enzymes secreted from various parts of tract to work with mechanistic
digestion to break down all of the nutrient
Simple Digestive Systems
Hydra
- Fresh water living organisms – very simple
- Standard tube with more tubes on top
- Digestive system: Only mouth, not anus
- Ingests food, takes it into middle of entity to digest food, before recirculating and regurgitating through its
mouth
- Not effective process – not all food will go down, as food goes down waste is coming up
Earthworm
- Through nature – evolved to get a through-gut – earthworm is a simple demonstration of this
o Essentially all higher organisms have this kind of system but different complexities in terms of what
the digestive system does and how it looks
- Food in through mouth → through digestive system → anus
The Pathway of Digestion
• The mammalian digestive (or alimentary) system is a hollow muscular tube with different structures down
- Brackets – accessory organs/glands helping helping in digestive tract, but not actually part of digestive tract
- Top: Buccal cavity/mouth (+ salivary glands – produce saliva; assists in digestion and breakdown)
- Pharynx
- Oesophagus
- Stomach
- Small intestine (+ pancreas, liver - enzymes)
- Large intestine (incl. caecum)
- Anus – elimination of any products
• Majority of action occurs between stomach and anus
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 18 - what, why and how of digestion. Autotrophs: require only inorganic compounds absorbed from the environment to make organic compounds, use solar energy (photosynthesis) to synthesise complex organic compounds for growth, do(cid:374)"t (cid:374)eed to eat a(cid:374)ythi(cid:374)g photosynthesis everything they need. Animals heterotrophs can"t synthesise organic compounds from inorganic molecules need to ingest them (hence have to consume nutrients we fundamentally need to survive) 3 classes of organic compounds consumed: animals classed on diet of these compounds. Amino acids for protein synthesis (enzymes, structural components of cells, etc) By product we need to excrete - urea. Other essential: things we need but cannot produce ourselves; depends on species. Vitamins and minerals important for processes such as enzyme parts, antioxidants, vitamins d (conditional bc get some from sunlight; also digest), b, c. Food you do(cid:374)"t (cid:374)eed (cid:373)u(cid:272)h of (cid:894)eg. donuts) for sugar and energy or if you eat paddock of grass (cow)
