A red blood cell has no nucleus and is therefore unable to make the proteins necessary to maintain itself. Because of this, red blood cells have a relatively short life span of about $120$ days. Given that we have about $25$ trillion red blood cells, show that more than $208$ billion red blood cells die and are replaced each day. Also show that, in the $20$ seconds it took you to read this problem, about $48$ million red blood cells died and were replaced.

What makes the “lub-dubb” sound of the heartbeat?

The body mass index (BMI) adjusts your weight for your height. You can calculate your BMI as follows:

$$\begin{aligned} \text { BMI } &=\frac{\text { your mass in kilograms }}{(\text { your height in meters })^2} \text { or } \\ &=\frac{\text { your weight in pounds }}{\left(\text { your height in inches) }{ }^2 \times 703\right.} \end{aligned}$$

What does BMI mean? BMI tells you if you are underweight or overweight.

How healthy is your diet? Write down everything you eat and drink for a day. Note the number of Calories when you can. About how many Calories do you consume per day? How does your diet compare to that recommended by MyPlate? What are you eating too much of? Not enough of?

Your heart rate is the number of times your heart beats in a minute. It changes over the course of the day as your activity level increases or decreases. Begin by measuring your resting heart rate. Ideally, you should do this when you first wake up in the morning. Now measure your heart rate during different types of activities. What is it when you're reading quietly? When you're walking or doing chores around the house? Finally, measure your heart rate while you are exercising. Are you hitting your target zone for effective cardiovascular exercise? You can determine your target zone by following these directions: First calculate your maximal heart rate: Maximal heart rate $=220-$ your age Then calculate your heart rate reserve: Heart rate reserve $=$ maximal heart rate

• resting heart rate You are in your target zone if you are using between $60 \%$ and $80 \%$ of your heart rate reserve:

Low end of target zone: $60 \%$ (heart rate reserve)$+$ resting heart rate High end of target zone: $80 \%$ (heart rate reserve)$+$ resting heart rate

What are some potential problems with low-carb diets?

Do low-carb diets work? How do they help people lose weight?

How does exercise help you lose weight?

How does a low-Calorie diet help you lose weight?

Explain how hemoglobin’s oxygen affinity is affected by blood pH, and how this change in oxygen affinity is adaptive.

How many oxygen molecules can one molecule of hemo- globin carry?

What is the structure of hemoglobin? Which part of the hemoglobin molecule binds to oxygen?

What stimulates the heart to beat?

Oxygen moves from the alveoli in the lungs into the bloodstream through the process of (a) active transport. (b) endocytosis. $(c)$ diffusion. (d) exocytosis.