BILD 2 Midterm 1 FA2026

what is a unicellular organism? Name an example.

an organism that has 1 cell that performs all necessary functions. An example would be bacteria.

Define multicellular organisms

big organisms with a large biomass that are compossed of multiple cells

How does form and function impact multicellular organisms?

The organisms's cells differentiate into specialized cells whose form creates structures to carry out specific functions of the body.

What are the advantages to multicellularity?

1. specialized cells into structures

2. larger organisms

3. more complex systems

4. better control of their internal environment

What are disadvantages of multicellularity?

1. growth time

2. reproduction constraints

3. have larger nutrient/oxygen demands

4. use a lot of energy to maintain a stable internal environment with multiple parts

5. communication of different organ systems is required

What are the 3 challenges to multicellular life? What is the main one?

1. Main challenge is to provide all cells with the necessary materials to function and to remove waste

2. materials must cross membranes

3. the transportation through membranes limits the rate at which materials can move

Surface Area-Volume ratio of a circle (formula and relationship)

Formula: S/V= 3/r

Relationship: r INC = S/V DEC

How does surface area-volume ratio impact the exchange of materials of a cell?

LARGE S/V ratio = more efficient exchange of materials

SMALL S/V ratio = harder to exchange of materials→ more material conservation

S/V ratio formula and relationship of a cube:

Formula: 6/x or 6x^-1
Relationship: if x increases, S/V would decrease

How can a growing organism increase in size while maintaining the required large surface area/volume ratio to perform its multicellular functions?

Membrane folds would increase surface area while keeping total volume constant, which would increase S/V ratio

Why is shape important to S/V ratio and material exchange?

Shape dictates the size of an organism, smaller or larger, which would then impact the S/V ratio to determine metabolic demands and the efficiency of material exchange

Define homeostasis?

the maintenance of constant conditions in the internal environment within a small range

Why is homeostasis important?

the internal environment of an organism must be kept within a homeostatic range or it can effect physiological variables on proteins structure and cell membranes which would affect enzyme activity and cell function

organisms regulate their internal environment through _____ _____.

Feedback loops

What is a thermal regulator? Provide an example.

an organism that maintains their internal temperature at a constant range. An example would be an otter.

What is a thermal conformer? Provide an example

An organism that can change their internal temperature according to its environment. Ex. Bass

Feedback loop structure

• animals that maintain homeostasis maintain their controlled variables at a set point

• a fluctuation above or below that set point is a stimulus

• the stimulus is sensed by a sensor

• the sensor communicates with the control center (which regulates the controlled variable) to incite a change

• the control center commands an effector to reverse the change to the controlled variable

Which of the following is a feedback loop and which is not and why?

1. Change in X → Change in Y → Change in Z

2. Change in X → Change in Y → Change in Z → Back to X

2 is a feedback loop because the change in Z causes a change in X. 1 is not a feedback loop because there is no return to X.

What does a negative feedback loop do? What does a positive feedback loop do?

Bonus: how do you identify each?

Negative:

• reverses a change in a variable to the opposite direction→ maintains homeostasis

• odd number of negative signs and a reverse in a physiological variable shows that it is a negative loop

Positive:

• amplifies a change in a variable/keeps a variable flowing in the same direction

• the absence of negative signs or an even amount signifies a positive loop

Describe the feedback loops for body temperature

1st:

• Stimulus: body temperature drops

• Sensors: Thermoreceptors→ skin and brain

• Control Center: hypothalamus compares to set point and sends signals

• Response: Blood vessels, muscles, sweat glands→ Shivering or vasoconstriction

• Controlled variable: body temperature increases

2nd:

• Stimulus: body temperature increases

• Sensors: Thermoreceptors→ skin and brain

• Control center: hypothalamus compares to set point and sends signals

• Response: Blood vessels, muscles, sweat glands→ sweating or vasodilation

• Controlled variable: body temperature decreases

Describe the feedback loop for blood pressure

Stimulus: stress

Controlled variable: blood pressure increases

Sensor: baroreceptors alert brain

Integrator/Control Center: brain sends nerve impulses to effector

Effector: heart

Response: Heart lowers BP

Describe the feedback loop for child birth:

stimulus: contractions increase

Controlled variable: cervix stretches

Receptors: nerves sense the cervix is being stretched

Control Center/Integrator: brain releases oxytocin

Effectors: muscles in the wall of the uterus contract more forcefully

Response: baby’s body stretches the cervix more

the stretching of the cervix causes the continuous release of oxytocin

How can you determine if a variable is homeostatically regulated?

1. plug it into the structure of the homeostasis feedback loop: stimulus→ sensor→set point/control center→effector→controlled variable

2. think about the loop and how the variable changing could return to normal (if it can return to normal then it is likely regulated)

Define thermoregulation. Why is it important?

Definition: the mechanism by which animals maintain their body temperature within a normal range

Importance: it affects enzymatic relations and can alter cell membranes

What are the 2 classifications that identify whether an animal controls its internal body temperature (regulation)?

1. thermoregulator

2. thermoconformer

What are the 2 classifications that identify where an animal gains their body heat from?

1. Endotherms: generate heat by their metabolism

• Ex. birds and mammals

1. Ectotherms: gain heat from outside sources

• Ex. fishes, frogs, turtles, snakes, reptiles

What are the pros and cons to being an endotherm? What about ectotherm?

Endo Pros:

• maintain stable body temperature despite environmental changes

Endo Cons:

• energetically expensive

Ecto Pros:

• requires less food

• can tolerate a greater variation in internal temperature

• still thermoregulate behaviorally (ex. basking, panting, or adaptations in body such as pigment)

Ecto Cons:

• heat drops when they do not have a source of heat (ex. at night) so activity drops

What are the 3 classifications that show how stable an animal’s body temperature is?

1. Poikilotherm: internal body temperature varies with its environment

2. Homeotherm: internal body temperature is constant

3. Heterotherm: An animal with a steady temperature at some times or in some body parts (endothermic), but variable at other times or in other parts (ectothermic)

What is the difference between a temporal heterotherm and a regional heterotherm?

Regional: ectotherms that can have high blood temperature via muscular activity while peripheral tissues are close to environmental temperatures (ex. tuna)

Temporal: temperatures that vary broadly over time→ they raise their temperature via muscular activity

Regional Heterotherms retain heat by:

1. having a low S/V ratio to conserve heat

2. Rete Mirabile→ counter current heat exchange mechanism

What is an advantage to being a regional heterotherm?

high metabolism in specific parts of the body allows them to have more energy for hunting

What three independent questions can you ask about any animal's thermal biology?

Where does the heat come from? How much does the temperature vary? Does it actively control the temperature?

Source (ecto/endo), pattern (poikilo/homeo/hetero), and control (regulator/conformer). Each animal gets one answer to each question, and the answers combine freely.

How can animals LOSE heat? Which is the most effective?

1. Radiation to a cooler object

2. Evaporative cooling (sweating)

3. Convection of cooler surrounding medium

4. Heat transfer by contact with a cooler sufrace

Sweating is the most effective

Heat exchange with the environment takes place across the surface of ___ ____. Heat is produced within the ____.

the body; body’s core

Heat is transferred in the body by the ____ system.

circulatory

Define vasodilation and what it does.

Definition: expands the blood vessels beneath the skin to transfer heat from the core to the environment

How do animals GAIN heat and CONSERVE heat?

Gain:

1. radiation

2. contact

3. metabolic reactions (ex. shivering and non-shivering)

Conserve:

1. unstirred layer: an insulating boundary layer. (feathers or fat)

2. Vasoconstriction: making the blood vessels in the body smaller to decrease S/V ratio and prevent heat from escaping

Define Shivering vs. Non-Shivering

Shivering: movement in the body to increase body temperature via metabolic reactions

Non-shivering: brown fat (creates heat

How do vasoconstriction and vasodilation relate to surface area-volume ratio?

VC: decreases the ratio to limit the exchange of heat from the blood/body to the environment

VD: increases the ratio to allow heat to escape the body

What is Rete Mirabile?

a counter current exchange system where capillaries with opposite blood flow of venous and arterial blood flow close to each other to exchange heat.

What is the purpose of rete mirabile?

to prevent heat loss to the periphery; warm blood coming from the core to the periphery and coold venous blood (in the case of dolphins) moving from the periphery to the core. It prevents cold blood from reaching the core to maintain body temperature of the core in homeostasis.

In a dolphin’s rete mirabile system the venous blood is ____ and the arterial blood is ____.

Cold; warm

In the case of Tuna (regional heterotherms) how does their rete mirabile differ from a ectothermic fish like trout?

they have an unstirred layer of fat in their gills which prevent them from losing heat to the water, trout dont have this. Their rete mirabile also conserves heat HOWEVER their venous blood warm and unoxygenated while the arterial blood is cold but oxygenated, which is the opposite of a dolphin’s rete mirabile.

what makes the Opah endothermic?

a mutation of fat in the gills that insulates their body which retains heat during breathing, a countercurrent system (rete mirabile), and a low s/v ratio

What are the 3 components of the endocrine system?

1. endocrine glands secrete hormones into the blood

2. causes gradual changes through the circulatory system

3. creates a slow but lasting response

What are teh 4 types of cell communications? Describe them

P- Paracrine: hormone targets nearby cells

A- Autocrine: a hormone acts on itself

N- Neuroendocrine: a neuron releases a hormone/communicator in the blood

E- Endocrine: gland secretes a hormone/communicator into the blood

Define Hormones and their key characteristics

Definition: chemical signal secreted by a cell or group of cells

Characteristics:

1. transported in the blood

2. activates physiological responses at low concentrations

3. binds to cell receptors to initiate biochemical responses

How can 1 hormone act on multiple tissues with varying effects?

the hormone must bind to hormone-specific receptors. The receptor determines the effect of the hormone.

Name 4 systems that hormones are used in? (CRRD)

1. Circulatory

2. Reproductive

3. Renal

4. Digestive

What are the 2 types of hormones?

Water-soluble (hydrophilic, lipophobic) and Lipid-soluble (hydrophobic, lipophilic)

What are the 3 classes of water-soluble hormones?

1. Peptides→ Oxytocin and ADH

2. Polypeptides→ Insulin and Human Growth Hormone

3. Amines→ Epinephrine

What are the 2 types of lipid-soluble hormones?

1. Amines→ Thyroid hormones (T3 and T4)

2. Steroid hormones→ Cortisol, estrogen, testosterone, progesterone

Name the 4 main locations where hormones are synthesized and their hormone

1. Hypothalamus→ Oxytocin and ADH

2. Pituitary Glands→ 6 hormones: CRH, ACTH, TSH, GH)

3. Adrenal gland→ epinephrine

4. Thyroid Gland→ T3 and T4

Water soluble hormones can travel through blood without _______. They cannot __________. They bind to _____ in the cell.

a transporter; enter the cell membrane; membrane receptors

Lipid-soluble hormones can travel through blood with ______. They can diffuse through _______. They bind to _____ or ______inside the cell. They can cause ____ change.

a transporter; the lipid bilayer; cytoplasmic or nuclear; genetic

What are the 3 steps that a hormone must undertake to get a response?

1. reception→ must bind to a hormone-specific receptor

2. signal transduction→ it must be translated via a signal transduction cascade

3. response→ activation of cellular response such as gene expression or cellular signaling

How can the same hormone have different effects on different cells?

1. the receptor is different

2. the signal transductions are different

either/or

What 3 main control centers compose the hypothalamus-pituatary axis? What is their function?

1. hypothalamus: receives information from other parts of the brain and initiates a response by secreting hormones

2. anterior pituitary gland: the true endocrine gland; makes and secretes hormones in response to hypothalamic hormones

3. posterior pituitary gland: stores the hormones that the hypothalamus makes (oxytocin and ADH)

True or false: the hypothalamus-posterior pituitary gland has a vascular connection.

FALSE: they have a neuronal connection

TRUE OR FALSE: the hypothalamus-anterior pituitary gland has a neural connection.

FALSE: they have a vascular connection

what do the hormones stored in the posterior pituitary gland do?

Oxytocin: regulates contractions during child birth and milk secretion

diuretic hormone: regulates water reabsorption in the kidneys + smooth muscle contractions in the kidneys (makes you pee)

what are teh 3 steps required for a response in the Anterior Pituitary Gland?

1. the hypothalamus releases a torphic hormone to the anterior pituitary gland

2. the anterior pituitary gland sends it’s stimulating hormones (the 6) to the target

3. the target reacts to the hormone and initiate the responses

What are teh 6 hormones secreted by the anterior pituitary gland

1. ACTH

2. Prolactin

3. TSH

4. GH

5. LH

6. FSH

What is the pathway for Cortisol via the anterior pituitary gland?

Hypothalamus secretes CRH

Anterior pituitary gland secretes ACTH

Adrenal cortex releases cortisol

Cortisol begins stress response to the target tissues

• ACTH regulates the hypothalamus

• Costisol regulares the hypothalamus and the Anterior pituitary gland

What is the pathway for Thyroid hormones via the antetior pituitary gland?

hypothalamus releases TRH

anterior pituitary gland releases TSH

thyroid gland releases T3 and T4

T3 and T4 travel to the target tissues

What do thyroid hormones effect (4) (GMPT)

1. metabolism

2. Growth and development

3. temperature regulation

4. protein synthesis

Describe the feedback loop for body temperature regulation by the thyroid

1. Hypothalamus releases TRH

2. Anterior pituitary releases TSH

3. Thyroid releases T3 and T4

4. T3 and T4 affect metabolism

5. Metabolism dictates body temperature

Body temperature is regulated by hypothalamus

T3 and T4 are regulated by Hypothalamus

TSH is regulated by hypothalamus

Name the 2 thyroid pathologies

1. Hypothyroidism

2. Hyperthyroidism

What element do T3 and T4 rely on and how do we obtain it?

Iodine obtained via diet

Describe and define Hypothyroidism and its symptoms

Definition: lack of thyroid hormone (ex. Goiter)

Symptoms:

• low metabolism

• weight gain

• feeling tired and cold

• memory and concentration problems

• stunted growth

• intellectual disabilities

• developmental concerns

Name 4 causes of hypothyroidism

1. Iodine deficiency

2. Thyroditis (“-itis” means swelling)

3. Hashimoto’s thyroiditis

4. Pregnancy hypothyroidism

Describe and define hyperthyroidism and its symptoms

Definition: excess thyroid hormone

Symptoms:

• nervousness

• irritability

• anxiety

• low heat tolerance due to high metabolic rate

• weight loss

• frequent bowel movements

• fine brittle hair

Name 3 common causes for hyperthyroidism

1. Grave’s disease

2. Toxic adenoma

3. Thyroidits

What are the effects of stress on the body? (6 of them)

1. no sleep

2. increased blood pressure and heart rate

3. sweating

4. anxiety

5. low appetite

6. learning problems

Describe the stress pathway in the endocrine system

1. stress stimulus is sensed by the hypothalamus

2. hypothalamus releases a hormone to the anterior pituitary gland

3. the anterior pituitary gland releases ACTH

4. ACTH arrives at the adrenal cortex

5. Adrenal cortex releases Cortoids

What do cortoids do?

• fight or flight response for the endocrine system stress response

• increases blood pressure and volume

• breaks fown fat and proteins and conserves glucose for energy

• suppresses the immune system

Describe the neural pathway for stress

1. stress stimulus is sensed by the hypothalamus

2. hypothalamus sneds a nerve impulse to the spinal cord

3. neuron is sent to the adrenal medulla

4. the medulla releases epinephrine and norepinephrine to trigger a stress response

What do ephineprhine and norepinephrine do?

• hormone and neurohormone of the neural stress response

• increase blood pressure and heart rate

• increase in breath frequency

• breakdown glucose

• change in blood flow patterns effects digestion