1. Lecture #6 Ms. Day/ Honors Biology
Organization of Life &
Homeostasis
Lecture #6
Ms. Day/ Honors Biology

2. What are Cells?
Definition: basic unit of structure and function of life
Although ALL living things are made of cells, organisms may be:
Unicellular – composed of one cell
Multicellular- composed of many cells

3. Multicellular Organisms
Cells in multicellular organisms often specialize (take on different shapes & functions)

4. Cell Specialization = DIFFERENTIATION

5. Cell Differentiation Do all cells look alike? NO!!!
Do all cells have the same functions?
Cell Differentiation
Process by which unspecialized cells (stem cells) develop into different cell forms and functions

6. How Do Cells Specialize Their Functions?
Cells in multicellular organisms become specialized by turning ON or OFF different genes different parts of their DNA

7. Levels of Organization
How are living things organized?
Chemical
Cells
Tissues
Organs
Systems
Organism

8. Organism Organization
Chemical
Atoms, molecules, compounds
Cell
Basic unit of living things
Tissue
Similar cells doing specific function
Organ
Similar tissues performing specific task
Organ System
Organs working together
Organism
All systems working together

9. Four Basic Types of Tissues
groups of cells similar in structure and perform common or related functions
Epithelial Tissue
Skin, lining of tissues
Connective Tissue
Blood, bones, cartilage
Muscle Tissue
Smooth, striated, cardiac
Nervous Tissue
Nerves and fibers

11. What is Homeostasis? Process that occurs in ALL living things
All organ systems work together to achieve homeostasis
Definition:
The ability of an organism to maintain its internal environment despite changes to its internal or external environment

12. Homeostasis in Animals
What do animals need to keep constant/healthy?
Body cells work best if they have the correct
Temperature
Water balance
Blood Pressure
Blood pH level
Glucose (sugar) levels
Oxygen and Carbon Dioxide Levels
How does an organism respond to these changes?
2 different pathways
Negative or Positive Feedback

13. Negative Feedback It ensures that small changes don’t become too large
Process that activates body to RESTORE conditions to their ORIGINAL STATE
Counteract further change in the same direction
STOPS THE CHANGE!
It ensures that small changes don’t become too large
MAINTAINS HOMEOSTASIS
EX: Thermoregulation, Blood sugar levels, Blood Calcium level, O2/CO2 levels in blood

14. Positive Feedback Allows for small changes to become too large
Process that activates body to AMPLIFIES original change
CONTINUES more change in the same direction
INCREASES the change!
Allows for small changes to become too large
DOES NOT MAINTAINS HOMEOSTASIS
EX: Uterine contractions, Lactation, blood clotting

15. Homeostasis Control Systems
3 components:
Receptor
Control Center
Effector
detects a change in some variable in the organism’s internal environment, such as a change in temperature
control center
processes the information it receives from the receptor and directs an appropriate response by the effector
Receptor
Control Center
Effector
Normal balance
Change in balance

16. Homeostasis Example: household thermostat
Receptor- Thermometer
Detects decrease in temperature
Control Center- Thermostat switches on furnace
Regulator- Furnace
Thermostat detects temperature increases over “normal”
Furnace turns off
Whole control system is called a negative feedback system

17. Negative Feedback Example #1: Thermoregulation in the body
What happens when you are too hot?
Sweat (liquid) turns to gas  requires HEAT
Heat comes from your body/skin  skin cools down

18. Negative Feedback Example #1: Thermoregulation in the body
What happens when you are too cold?
“Goose Bumps”
hairs trap a layer of air next to skin  warms by body heat
Air becomes an insulating layer
Called piloerection
Shivering
Muscle movements use ATP (energy)
Breaking ATP releases HEAT

19. Maintaining Body Temperature (Thermoregulation)
Humans have a normal temperature of around 36.2 to 37.2 °C (98.6°F)
If your body temperature goes above normal temperature  likely suffering from infection
your body raises its temperature to fight off the infection
If your body goes below this range it indicates hypothermia.
could lead to cell damage and possibly death.

20. Negative Feedback Example #2: Regulating Blood Sugar (Glucose) Levels

21. Negative Feedback Example #3: Regulating Calcium Levels in Blood
Why do you need calcium?
Carries messenges in body
Muscle contractions
Nervous system homeostasis
Bone/teeth formation
Helps blood clotting

22. Negative Feedback Example #4:Regulating Oxygen and Carbon Dioxide Levels in Blood
O2 / CO2 level returns to normal
Holding breath,
CO2 levels rise
Control system forces exhale, inhale

23. Positive Feedback Example #1: Uterine Contractions
During childbirth…
Baby’s head PUSHES against sensors near opening of uterus
Oxytocin (hormone) is released  stimulates uterine contractions
More contractions  more oxytocin
ONLY STOPS when pushing STOPS

24. Positive Feedback Example #2: Lactation (making milk)
Suckling by baby stimulates brain to release hormone (prolactin)
Prolactin makes milk
More suckling by offspring (baby)  more milk production

25. Positive Feedback Example #3: Blood Clotting
Damaged blood vessel stimulates release of clotting factors  Platelets build up at injured site
More chemicals released  more platelets
Platelets continue to pile up and until clot is formed
Finally, growth hormones stimulate cell division
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot

26. Homeostasis in Plants What do plants need to keep constant/healthy?
Plant cells work best if they have the correct
Water
Sunlight
Oxygen and Carbon Dioxide Levels

27. Homeostasis in Plants
What mechanisms for plants use to help maintain homeostasis?
Creates a waxy cuticle on leaves
Stores extra water
Opening/closing of stomata (pores in leaves)
Bends towards light

28. Homeostasis in Plants Using Stomata
Guard Cells
What do plants use to control gas exchange?
Guard Cells & Stoma
Why do plants need to OPEN stomata?
Photosynthesis
Making food
If the plant needs water for photosynthesis, why is water coming out of the stomata?
Losing H20 helps get H20 up plant against gravity!!
What goes out? O2
H2O
CO2
What goes in?
Stoma Closed
Stoma
Stoma Open

29. Homeostasis in Plants Using Stomata
Why would the plant close stomata using guard cells?
Prevent excess water loss (conserve water)
So what is the point of having stomata?
Remove waste gas (O2)
Take in gas (CO2) for photosynthesis
Help move water up plant for photosynthesis
Control water loss
Guard Cells
Guard Cells
Stoma Open
Stoma Closed
Guard cells open by inflating with extra water. They do this by pumping K+ ions into the cell, which causes water to rush in via osmosis to diffuse the high ion concentration.

30. More Homeostasis in Plants
Stems bend towards sunlight to maintain the amount of photosynthesis.
Called phototrophism
Stems store extra water in a huge “pool” inside their cells
Called a central vacuole