- When one muscle contracts and shortens it creates tension (pulling force) that elongates the relaxed muscle allowing flexion or extension around the joint

Earthworm – hydrostatic skeleton

Antagonistic Muscles

- Longitudinal muscles

-Run length of body from head to anus

-when longitudinal muscles contract, body diameter widens (or circular muscles relax)

- Circular muscles

-Encircle body around circumference

-longitude muscles relax when circular muscles contract

-when circular muscles contract, the diameter narrows

How Muscular antagonism works in exo/endo skeletons

- Vertebrates and arthropods have jointed skeletons

- Muscles are attached to the EXTERIOR of the endoskeleton or INTERIEOR of the endoskeleton

- Antagonistic muscles relax and contract to facilitate flexion and extension around joints

Lecture 13 (Feb. 27, 2025)

Moving Molecules

Molecular Motion

- Diffusion – movement of a population of molecules from a high concentration to a low concentration (SOLUTES)

-Movement of molecules down their concentration gradient

- Keep moving until equilibrium is reached

- Net movement – movement in a particular direction

- Molecule movement is spontaneous – no energy required (passive)

Will individual molecules stop moving when the solution reaches equilibrium?

- No, net movement of the population stops but individual molecules keep moving

- Avg. rate of molecules crossing in each direction is equal

- Regardless of movement, equilibrium will always be maintained (Dynamic equilibrium)

-ex. there are 5 purple molecules on right, and 5 yellow on left. If one purple moves to left, one yellow will move to right. No net movement is occurring but equilibrium is maintained.

Membrane Structure and Function

- All cells must control their internal environment

- All enclose compartment is requires to,

-concentrate materials

-bring reactants together

- Cell membrane = the barrier between cells and their environment

- The plasma membrane of cells is composed of a double layer of phospholipids

-the phosphate heads face the inside and outside of the cells which have liquids because the lipid tales cannot go in the liquids

- Cell membranes are selectively permeable

-some molecules move directly between phospholipids, others cant cross at all

Simple Diffusion

- Occurs when molecules move from areas of high concentration to areas of low concentration directly across a cell membrane

- i.e. molecules move down their concentration gradient to enter or exit a cell

- some molecules, like water, can move directly across a selectively permeable membrane

-water diffusion = osmosis

- Some molecules cannot move directly across a selectively permeable membrane

Osmosis

- Osmosis is a special case of diffusion; in this case there is movement of WATER molecules

- Occurs when the movement of molecules other that water is blocked by a selectively permeable membrane

- In osmosis, water moves from an area of LOW SOLUTE concentration to an area of HIGH SOLUTE concentrations

Solutions (solute mixed with water)

- Solutions slide 1: reread and understand what is said

- If we are comparing two solutions, then we can describe one of the solutions as:

-Hypotonic if it has a LOWER solute concentration than the other solution

-Isotonic if it has the SAME solute concentration as the other solution (equilibrium)

-Hypertonic if it has a HIGHER solute concentration than the other solution

- (look at picture on phone for answer + explanation to next 2 slides)

Predictions

- For each animal cell shown below, indicate whether he surrounding solution is isotonic, hypertonic, or hypotonic relative to the inside of the cell

-1=hypotonic, 2=isotonic, 3=hypertonic

-Net movement of water from a hypotonic solution to a hypertonic solution.

Osmosis question:

- When does the net diffusion of water into or out of a cell stop?

-When solute concentration reaches equilibrium between inside and outside

- In this example, could that state ever be reached?

-No because there is solute in the balloon and none outside. Water keeps moving into the cell because there will always be more solutes inside than outside and the cell membrane is not rigid enough to resist stretch.

- Semi permeable membrane is introduced to the balloon.

-What would eventually happen?

-Water moves in the balloon expands until the walls of the box (semi permeable membrane) prevent further expansion. No explosion.

Predictions (again)

- Plant cells do not respond the same as animal cells to hypotonic, hypertonic, and isotonic solutions because the cell membrane is surrounded by a cell wall

- Under normal physiological conditions, the extracellular fluid in plants is hypotonic.

-This maintains the turgid condition of the cell that provide structural support to non-woody tissues

- PLASMOLYZED…what does this mean?

-Process in which cells lose water in a hypertonic solution

- During plasmolysis, the protoplast (equivalent to cytoplast), which is surrounded by a plasma membrane, shrinks away from the cell wall.

- Plasmolysis does not occur in animal cells as they do not have cell walls.

Facilitated Diffusion: Passive Transport Aided by Proteins

- Still passive because a concentration gradient is still present

- Not all molecules can diffuse directly across the plasma membrane

- Large molecules like sugars cannot cross (sugar is needed for ATP)]

- Charged molecules including ions like Na⁺, Cl^-, etc. cannot cross.

- They diffuse through transport proteins (transmembrane proteins)

- Facilitated Diffusion: molecules still move down their concentration gradient across a plasma membrane through transport proteins

- Example of transport proteins: Aquaporins

- This process does NOT require energy to happen because they are moving down their concentration gradient which IS required

Passive and Active Transport

- Passive transport: the movement of a population of molecules from areas of high concentration to areas of low concentration

-Energetically this is like a ball going DOWN a slide

- Active Transport: The movement of a population of molecules from areas of low concentration to areas of high concentration

-Energetically this is like a ball going UP a slide

-In active transport molecules are moved AGAINST the concentration gradient

-Requires energy in the form of ATP

Steps to active transport (find video and review to better understand)

- Start by binding solutes to binding sites in transport protein (binding sites are same shape as solutes)

- Energy (ATP) is used to change the shape of the protein. Phosphate will stay bound will the solutes get to the outside of the cell. The ATP is not needed and will be released

- The solute is released on the other side of the membrane. The shape of the protein changes and the shape of the binding site are also changed making the solutes able to be released

- The protein returns to its original shape

Active transport requires

- A selectively permeable membrane

- Transport proteins (embedded in the plasma membrane)

- ATP

Lecture 14

Gas Exchange in Plants

Gas Exchange

- Is the process by which organisms:

-uptake gasses required for physiological processes

-release waste gasses (by-products) of those processes

- Photosynthesis:

-Uses CO2 and H2O

-Produces sugars and O2

- Cellular Respiration:

-Uses sugars and O2

-Produces ATP + CO2 and H2O

- QUESTION ANS: Simple diffusion; CO2 and O2 move directly across the membrane (look at photo)

Diffusion

- What can we conclude about the rate of diffusion given these data (refer to slide)

-The greater the distance, the more time it takes for diffusion to occur across all cells

-Diffusion is efficient at the cellular level but too slow to support physiological process over long distances

- QUESTION ANS: A; large surface area for a small volume

-Surface area to volume ratio is higher for smaller organisms

-more cells are close to the surface; shorter distance for diffusion

CONCLUSION: Diffusion is only good if the diffusion is short

- QUESTION ANS: C; significantly more SA even though all the volumes are the same (look at photo for full answer)

Surface Area to Volume Ratio

- Both shape and size affect the SA to vol. ratio.

- For a given volume, flattened shapes have a greater SA

- The picture in the slide shows that even though both shapes had the same volume, the flatter one has more SA since more of it is in contact with the environment during gas exchange

- Structures and whole organisms adapted for exchange by diffusion maximize SA through:

-Flattened shape

-Folded surface

-Branching

-Projections

- What is the primary exchange and transport mechanism in these plants (bryophytes)

-Diffusion – they didn’t have a choice because they didn’t have vascular systems (non-vascular plants)

- Where does gas exchange occur in trees?

-Gasses are not transported long distances in plants

-gas exchange is important for cellular metabolism; all living cells need to exchange gasses

-adaptations must have happened to ensure gases can move in and out of cells quickly

Stomata Structure and Function

- Structure

-Pores in the leaf and other photosynthetic surfaces.

-all parts of the plant that are green have stomata; not only in leaf

- Function

-Stomata are the passageway for the diffusion of gasses through the waxy cuticle (no waxy cuticle is present where the stomata is)

- he CO2 required for photosynthesis enters a leaf, and the resulting O2 exits via stomata

- Guard cells

-two cells that flank the stoma and control whether it is open or close to the surrounding environment

-Guard cells change shape in response to water loss and uptake

-Shape change results in opening and closing of the pore

TURGID GUARD CELLS = OPEN STOMA

-Stoma closes in hot environments

- Attached at the tips:

-Open when the water enters the guard cells and fill the vacuoles

-Turgiud cells bow outward, opening stomata

-When gurad cells lose water, the stomata flattens and closes

IMPORTANT – GO OVER NOTES AND PHOTO OF SLIDE

The chain of reactions that cause water to enter or leave the guard cells is stimulated by changes in environmental contitions

If CO2 is low, photosynthesis has used it all

O2 is too high, by-product is high and needs to be expelled

Stomata needs to facilitate entry of CO2 and exit of O2

Cactus have adapted

At night – open stomata, uptake CO2, stores it, then closes

In day – they stay closed, but release CO2 in sunlight

Leaf Structure

- The leaf epidermis is covered by a waxy cuticle except where it is interrupted by stomata

- The leaves ground tissue called the mesophyll, is sandwiched between the upper and lower epidermis

- Mesophyll consists mainly of parenchyma cells which are specialized for photosynthesis

- 2 distinct layers in Mesophyll:

1. Palisade mesophyll: elongated, 1 or more layers of parenchyma cells on upper epidermal layer

2. Spongy Mesophyll is below the palisade mesophyll

- These parenchyma cells are arranged loosely allowing free circulation of CO2 and O2

More stomata on the surface = less water loss

Adaptations for Gas Exchange

- Green stems of young or non woody plants use stomate for gas exchange

- Gasses diffuse into the stems of woody plants through the pores in the bark called lenticels

- The major difference from stomata is that they do NOT open and close

- Older woody roots also have lenticles so that they can exchange gas through the bark covering the root

- Growing root tips have epidermal cell extensions called root hairs.

-Function: 30 Root hairs maximize surface area for gas exchange and water/nutrient uptake

- Good soils have air pockets where plants roots can exchange gases (Too much water = bad for plant bc no gas exchange can occur)

- What type or root adaptation allows access to O2 in waterlogged soils?

-Pneumatophores

Even though air is needed for gas exchange, plants adapted to Pneumatophores (which stick out of water) to help with gas exchange.

Lecture 16

Ventilation and Gas Exchange in Animals

Questions at beginning

1. A

2. D

3. B is worst, E is best

Gas Exchange Surface

- Recall the structure of the respiratory surface in a plant leaf

-Loosely packed mesophyll cells coated in a film of water

- To maximize diffusion efficiency, respiratory surfaces have the following characteristics:

-Thin

-Large SA – branches or folded (always in areas of absorption, ex. Small intestine)

-Moist (frogs have mucus on their skin for this purpose)

Why moist?

-Gases transfer more efficiently when they are dissolved first (hence why our noses have mucus since smell is gaseous)

Ventilation: Definition

- The flow of respiratory medium (air or water – the source of gaseous exchange) across respiratory surface (body, wall, lungs, gills – where gaseous exchange take place).

Gas Exchange and Ventilation

- Oxygen and carbon dioxide move into and out of cells by cellular respiration

- Suring cellular respiration, cells are constantly consuming O2 and producing CO2 as a waste product

- This means there will typically be more CO2 and less O2 in body cells compared to the air/water outside the body

- In order for gaseous exchange to take place at the respiratory surface, a concentration gradient must exist

- This steep concentration gradient drives the rapid diffusion of gasses between respiratory organs and air/water

- Cellular respiration uses sugar, water, and oxygen to produce energy in the form of ATP (end product of cellular respiration)

- Animal movement requires muscle contraction; muscle contractions use a lot of energy

- This means that fast moving animals (or animals that use more energy) need an effiecient way of accessing O2 in the air

Sponges

- Enviornment – Aquatic

- Respiratory medium – Water

- Respiratory Surface – Body wall

- Ventilation - collar cells beat their flagella to pull water through body pores

- Locomotion – sessile

Cnidarians

- Enviornment – Aquatic

- Respiratory medium – Water

- Respiratory Surface – Body wall and lining of gastrovascular cavity

- Ventilation – water is pulled in and circulated through GV cavity

-Gas exchange direct cell to cell

- Locomotion – sessile, weak swimming

Insectcs

- Enviornment – Terrestrial, some aquatic

- Respiratory medium – Mostly air

- Respiratory Surface – Tracheal system

-netwrok of air-filled tubes branching throughout the body (some aquatic species have gills)

- Ventilation

-Spiracles – air enters the tracheal system through openings called spiracles

-air entering the trachea pass into smaller tubes called tracheoles

-The branches tracheoles deliver air directly to cells throughout the body

-Small Insecs – air moves through the tracheal system through diffusion

-Large insects – can use muscles to expand and contract body segments like bellow

-pums air rapidly through tracheal system, supplying highly metabolic cells with adequate O2

-Air sacs – store air near critical organs, can hold reserve air for release while underwater

- Locomotion (definition)– The energy cost of flying, swimming and running (fast crawling, flying)

- Fast locomotion and flight require rapid gas exchange to support high metabolic rate of the working muscles

Vertebrates

- SA to volume ratio is too low and activity levels are too high in more vertebrates for efficient gas exchange across body surface

- Where does gas exchange typically occur in such animals?

-first at the lungs, then at the cells

- Respiratory organs

-internal structures that maximize SA through extensive branching or folding

-Lungs (facilitate gas exchange in air) and Gills (facilitate gas exchange in water)

-Animals whith speicalized repiratory organs also require circulatory system to transport gasses throughout the body

Fish

- Enviornment – Aquatic

- Respiratory medium – Water

- Respiratory organ – gills

- Respiratory surface – gill filaments

- Ventilation – water is pulled into the mouth and over the gill fragments (filled with capillaries) in ONE direction

-Blood flowing through capillaries withing the gill filaments oicks up O2 from the water

- Locomotion – Swimming

Gas exchange systems typically need to be more efficient in water than in air. Why?

1. Water has higher density than air therefore it takes more energy to mobe across respiratory surfaces comared ti ho air moved over lungs in terrestrical animals

-this is why fish require relatively large structures in contact woth the water to facilitate gas exchange

2. Water has about 40x less oxygen than equal volume of air

Countercurrent exchange (in fish) IMPORTANT NEED TO KNOW

- Blood flows one way, water flows the other

- Thes arrangement of capillaries in a fish gill allows for countercurrent exchange, the exchange of a substance between two fluids flowing in opposite directions

-This arrangement maximizes gas exchange efficiency

- Because blood flows in the direction opposite to that of water passing over the gills, at each point in its travel blood is less saturated with O₂ than the water it meets. (the water has more O2 than blood because a concentration gradient needs to exist for the O2 to go from water to blood)

- As blood enters a gill capillary, it encounters water that is completing its passage through the gill.

-The water at this point is depleted of much of its dissolved O2, but still has a higher PO₂ (partial pressure) than the incoming blood, and O₂ transfer takes place.

- As the blood continues its passage, its PO₂ steadily increases, but so does that of the water it encounters.

- Thus, a partial pressure gradient favoring the diffusion of O₂ from water to blood exists along the entire length of the capillary

- Low concentration O2 = blood entered the gills, high concentration O2 = water entered the gills

Summary:

- Oxygen rich water enters from the mouth into the gills

- Blood enters the gills

- O2 diffuses from water to blood since water always has a high O2 concentration

- Countercurrent flow maintains concentration gradient along the length of the blood vessel

- ~80-90% of O2 in water diffuses into blood

Ventilation and Gas Exchange: Mammals (humans)

- All air breathing vertebrates use lungs for gas exchange

- Lungs do not expand and recoil on their own

-In birds, lungs do not expand

-don’t contract cause lungs don’t have muscles

- Vertebrates have different mechanisms for moving air into and out their lungs

Mammals

Environment: Terrestrial or Aquatic

Respiratory medium: Air

-dolphins cant exchange gasses with water

Respiratory organ: lungs

Locomotion: walking, running, swimming, flying, hopping

Human respiratory system

Air enters the body by the following pathway:

1. Nostrils

2. Nasal cavity

3. Pharynx

4. Larynx

5. Trachea

6. Bronchi

7. Bronchioles

8. Alveoli

Air leaves the body by the same route in REVERSE

Respiratory Surface

- Alveoli: tiny expandable sacs that inflate upon inhalation and deflate upon exhalation

- Capillaries: Branching nets of fine blood vessels that surround and exchange materials (gasses) with alveoli

Negative Pressure Breathing

- Mammals create negative pressure inside the lungs by expanding chest

- Lungs are inflated by using negative pressure to pull air inside

- Boyles law: Volume increase = pressure decrease and vise versa

Ventilation In Mammals

- Inhalation

-Rib muscles and diaphragm contract

-Volume of lungs increase

-Pressure inside lung drops

-Air is pulled into lungs

-Lungs are inflated using negative pressure

- Exhalation

-Rib muscles and diaphragm relax

-Volume of lungs decreases

-Pressure inside increases

-Air is pushed out of lungs due to high pressure

Gas Exchange in Humans

- O2 and Co2 diffuse down their concentration gradients between air inside alveoli and blood inside the surrounding capillaries

- The greater the difference in O2 and CO2 concentrations between the air in the alveoli and the blood in the capillaries, the faster diffusion occurs

- Inhalation

-O2 concentration is higher in air in alveoli than in blood in capillaries

-CO2 concentration is higher in blood in capillaries than in air in alveoli

-O2 diffuses from alveoli into capillaries

-Co2 diffuses from capillaries to alveoli

- Exhalation

-Air with high [CO2] removed from lungs

Gas Transport in Humans

- Oxygen Transport

-Hemoglobin – a red protein in red blood cells that binds with O2 (have to mention red blood cells)

-O2 is transported inside red blood cells from the lungs to the body cells where it is required

- When oxygen rich blood reaches the capillaries surrounding body cells that have depleted O2 and high CO2 concentration: